arch/arm/src/stm32/stm32f33xx_adc.c:  Eliminate warnings about cj_channels and j_chanlist being set but not used.

Changes from review of clock_nanosleep():  Misplaced right bracket, but return value in one failure case.

sched/signal/sig_nanosleep.c and libc/time/lib_nanosleep.c:  Implement clock_nanosleep().  nanosleep() is now reduced to a libc wrapper around clock_nanosleep().

libc:  Add support for readv() and write(). Also includes some cosmetic changes to some unrelated files.

STM32L4 serial PM interface improvements

* stm32l4_serial: pm: check rx/tx buffers for pending data in pmprepare

* stm32l4: remove adhoc PM interfaces and move serial suspend functionality behind CONFIG_PM

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

tools/configure.sh: This commit adds a -m option for macOS. For anyone not aware, Apple renamed OSX to macOS recently; thus the 'm' instead of 'o'. This does not change the other uses of *_OSX to macOS.

lc823450 auto LED support

* arch/arm/src/lc823450: Add auto LED for CPU activity

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

* configs/lc823450-xgevk: Add auto LED support

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

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

drivers/usbdev/rndis.c: fix packet receiving logic.  The logic didn't take single-byte termination frames in account.

lc823450-xgevk audio support

* arch/arm/src/lc823450: Add IPL2 support

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

* configs/lc823450-xgevk: Add IPL2 support

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

* libc/audio: Fix compilation error in lib_buffer.c

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

* drivers/audio: Add WM8774 support

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

* arch/arm/src/lc823450: Add I2S support

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

* configs/lc823450-xgevk: Add WM8774 support

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

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

Add IPL2 support for LC823450

* arch/arm/src/lc823450: Add IPL2 support

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

* configs/lc823450-xgevk: Add IPL2 support

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

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

sched/sched/sched_cpuselect.c:  For SMP, In order to find the cpu with the lowest priority thread, we have to remember the already found lowest priority.  Noted by Anonymous in Issue #75

lpc43xx Ethernet:  Fix some backward logic setting full-duplex and 100mbps when autoconfiguration is disabled.  Noted by Anonymous in Issue #76

arch/arm/include/stm32 and stm32f7:  Remove ltdc.h and dma2d.h.  Those header files in that location permitted inclusion into application space logic and, hence, facilitated and encouraged calling into the OS and violating the portable POSIX OS interface.  The definitions in those header files were move the appropriate location in the counterpart, architecture specific files at arch/arm/src/stm32 and stm32f7 dma2d.h and ltdc.h.

configs/stm32f429i-disco/ltdc:  This configuration has been deleted because it violated the portable POSIX OS interface.  It used apps/examples/ltdc and include ltdc.h and dma2d.h which were also removed for the same reason.

fs/userfs:  Fix return value from dup method.  In order to return a pointer, the parameter must be a pointer to a pointer.

This comment converts the underlying IPC used by the UserFS from Unix domain local sockets to UDP LocalHost loopback sockets.  The problem with the local sockets is that they do require operations on the top level psuedo-file system inode tree.  That tree must be locked during certain traversals such as enumerate mountpoints or enumerating directory entries.

This conversion is unfortunate in the sense that Unix local domain sockets are relatively lightweight.  LocalHost UDP sockets are much heavier weight since they rely on the full UDP stack.  If anyone is up for a complete redesign, then using some shared memory and a POSIX message queue would be lightweight again.

This commit also fixes several bugs that were not testable before the inode tree deadlock.  I cannot say that the logic is 100% stable but it does not have basic functionality.

Squashed commit of the following:

    fs/userfs:  Order locking so that access to the shared I/O buffer is also locked.
    fs/userfs:  Converts to use LocalHost UDP loopback for IPC.