* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
sched/init/nx_start.c: Add support for CONFIG_BOARD_DRIVER_INITIALIZE. If this option is selected then nx_start() will call a board-provided function board_driver_initialize() immediately after calling up_initialize().
Rename CONFIG_BOARD_INITIALIZE to CONFIG_BOARD_LATE_INITIALIZE.
Raname board_initialize() to board_late_initialize()
sched/init/nx_bringup.c: Fix a naming collision.
sched/init: Rename os_start() to nx_start()
sched/init: Rename os_smp* to nx_smp*
sched/init: Rename os_bringup to nx_bringup
sched/init: rename all internal static functions to begin with nx_ vs os_