Fix SMP related bugs

* sched/sched: Fix a deadlock in SMP mode

    Two months ago, I introduced sched_tasklist_lock() and
    sched_tasklist_unlock() to protect tasklists in SMP mode.
    Actually, this change works pretty well for HTTP audio
    streaming aging test with lc823450-xgevk.

    However, I found a deadlock in the scheduler when I tried
    similar aging tests with DVFS autonomous mode where CPU
    clock speed changed based on cpu load. In this case, call
    sequences were as follows;

    cpu1: sched_unlock()->sched_mergepending()->sched_addreadytorun()->up_cpu_pause()
    cpu0: sched_lock()->sched_mergepending()

    To avoid this deadlock, I added sched_tasklist_unlock() when calling
    up_cpu_pause() and sched_addreadytorun(). Also, added
    sched_tasklist_lock() after the call.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* libc: Add critical section in lib_filesem.c for SMP

    To set my_pid into fs_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* mm: Add critical section in mm_sem.c for SMP

    To set my_pid into mm_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* net: Add critical section in net_lock.c for SMP

    To set my pid (me) into fs_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

Approved-by: Gregory Nutt <gnutt@nuttx.org>

libc/lzf:  Fix some typos in code that was in conditional logic that was not building.  Change a literal use of 13 to HLOG which used to be 13.

Squashed commit of the following:

    fs/cromfs:  Now depends on EXPERIMENTAL because it is not yet verified.
    fs/cromfs:  This commit brings the CROMFS file system to code complete.  Still completely untested.  Next steps:  Need a tool to generate CROMFS file system images and a test case under apps/
    fs/cromfs:  Add logic to traverse the in-memory file system nodes.
    fs/cromfs:  Add initial support for an in-memory, compressed, read-only file system.

configs/stm32f4discovery:  Building of stm32_appinit.c should not depend on CONFIG_NSH_LIBRARY but on CONFIG_LIB_BOARDCTL.

configs/stm32f4discover/posix_spawn:  With recent changes, needs to enabled boardctl() w/symbol table support.

libc/lzf:  lzf_compress() now expects the hash table as user allocated input parmeter rather than declaring the huge array on the stack.

(cherry picked from commit ea77dfafe1afe7d399e47871d2ec81fea99626cc)

(cherry picked from commit 8879116fe85558520c4811dc4ab780b28e66810d)

drivers/serial/Kconfig:  Kconfig is too big, divide into Kconfig, Kconfig-uart, Kconfig-usart, Kconfig-sci, Kconfig-16550.  More than one MCU supports LPUARTs.  Add Kconfig-lpuart and remove MCU-specific LPUART definitions.  Affects Kinetis and STM32L4.

arch/arm/src/stm32/lowputc: fix uart glitch when lowputc is enabled

Calling up_lowputc() when a character is in the shift register results
in corrupted character on stm32f1xx and stm32f205 cores.
TC status bit ensures that up_lowputc() waits for an on-going
transmission to complete before writing in TDR.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

stm32f103-minimum: add support for DFU bootloader

Approved-by: Gregory Nutt <gnutt@nuttx.org>

net/tcp:  In tcp_input(), add the logic to detect, decode, and respond to TCP Keep-Alive packets.  In tcp_timer(), fix some problems with the way that TCP Keep-Alive probes were being formatted.

arch/arm/src/stm32/usb: skip recipient check for descriptor related requests

Approved-by: Gregory Nutt <gnutt@nuttx.org>

    net/tcp:  Add logic to send probes when SO_KEEPALIVE is enabled.
    net/tcp:  TCP socket should not have to be connected to configure KeepAlive.
    net/: Add a separate configuration to enable/disable KEEPALIVE socket options.
    net/tcp: Arguments to TCP keep-alive timing functions probably should be struct timeval as are the times for other time-related socket options.
    net/tcp:  Fix a backward conditional
    net/tcp:  Add some more checks and debug output to TCP-protocol socket options.
    net/tcp:  Cosmetic changes to some alignment.
    net/:  Adds socket options needed to manage TCP-keepalive and TCP state machine logic to detect if that the remote peer is alive.  Still missing the timer poll logic to send the keep-alive probes and the state machine logic to respond to probes.

drivers/lcd/ft80x:  Fix a typo that caused the driver to fail to recognize the ft801 chip version. Also update an unrelated README file.