Merged in masayuki2009/nuttx.nuttx/lc823450_dvfs_auto (pull request #604)

lc823450 dvfs auto

* arch/arm/src/lc823450: Fix up_enable_irq() timing for I2S.

    In previous commit, I2S IRQ might be sometimes assigned to CPU1
    when CONFIG_SMP=y. This change fixes this issue.

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

* arch/arm/src/lc823450: Refactor timer driver.

    Introduce lc823450_timer.h and move lc823450_timerisr.c to
    lc823450_timer.c Add MTM timer APIs for DVFS.  Introduce
    up_rtc_gettime() for CONFIG_RTC_HIRES.

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

* arch/arm/src/lc823450: Introduce idle time calculation in DVFS

    Also, DVFS autonomous mode based on CPU idle time is supported.
    NOTE: voltage control is still disabled.

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

* configs/lc823450-xgevk: Update defconfigs

    Enable RTC_HIRES instead of RTC_DATETIME (audio/rndis)
    Disable TCP_WRITE_BUFFERS and change SCHED_LPWORKPRIORITY (rndis)

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

* configs/lc823450-xgevk: Update README.txt

    Update SMP and DVFS related part

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

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