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/: Convert legitimate uses of task_create() to nxtask_create(). Review handling of returned values from all uses of kthread_create() (as well as nxtask_create()).
graphics/: Review return values for all calls to kthread_start() because it no longer returns an errno.
drivers/: threads started by drivers should be kernel threads, not user tasks. Review return values for all calls to kthread_start() because it no longer returns an errno.
configs/: threads started by board bringup logic should be kernel threads, not user tasksi (part 2 of 2).
sched/task: Add nxtask_create(). Kthread_create() and nxtask_create() are internal OS functions and should not modify the errno variable. configs/: threads started by board bringup logic should be kernel threads, not user tasks.
Squashed commit of the following:
configs: Each board now initializes the touchscreen controller as a normal part of its board bring-up. board_tsc_setup() is gone; the touchscreen controller is now treated like any other on-board device.
Remove all support for BOARDIOC_TSCTEST_SETUP
Move prototype for board_tsc_setup() from include/nuttx/board.h to individual board header files.
drivers/video: fb driver now clears framebuffer initially. Eliminates (or minimizes) initial garbage on the display.
configs/open1788: Initialization now follows the pattern of other boards. Add initialization of fb driver.
configs/open1788: Add a configuration for testing the framebuffer driver.
