nitrogen6_scm: initial addition, Boundary Devices board

nitrogen6_scm: setup rgb_gpio_pads in board_early_init_f
nitrogen6_scm: nitrogen6_scm_defconfig add CONFIG_BLOCK_CACHE
nitrogen6_scm: use common code for eth init
nitrogen6_scm: eth.c now in common directory
nitrogen6_scm: move misc_init_r/do_kbd to common
nitrogen6_scm: move max77823_init to common
nitrogen6_scm: move mmc_init/ dram_init/ overwrite_console/ common_board_init/ splash_screen_prepare/ board_cfb_skip to common
nitrogen6_scm: normal display support
nitrogen6_scm: change # of mmc/sdcards to 1
nitrogen6_scm: add  CONFIG_SPI_FLASH_GIGADEVICE: to defconfigs
nitrogen6_scm: port to v2018.07

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

nitrogen6_scm: update m4 support for FreeRTOS
nitrogen6_scm: add secure boot option
nitrogen6_scm: update to v2017.01
nitrogen6_scm: update to v2017.03

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>