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()
stm32f746g-disco: touchscreen support
* fixed FT5x06 driver to correctly close (previously it unregistered interrupt handler during close)
* added LittlevGL demo for STM32F746G-DISCO
Approved-by: GregoryN <gnutt@nuttx.org>