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()
configs/stm32f4discovery/include/board.h: Add SPI DMA pins definitions to get CS43L22 audio DAC working
configs/stm32f4discovery/audio: Add board configuration for CS43L22 audio example
configs/stm32f4discovery: Update README