nitrogen7: initial addition, Boundary Devices board

nitrogen7: add CONFIG_CMD_GPIO
nitrogen7: change qspi to 25Mhz
nitrogen7: rename imximage.cfg to nitrogen7.cfg
nitrogen7: add linking at qspi offset of 0x1000 option
nitrogen7: add qspi parameter config
nitrogen7: add CONFIG_SPI_FLASH_WINBOND
nitrogen7: rename qspi-param to qspi-sst25vf016
nitrogen7: qspi-W25Q128BV initial addition
nitrogen7: use boundary.h
nitrogen7: add cmd_custom=echo to avoid upgrade message
nitrogen7: add wlmac environment variable
nitrogen7: fix wlmac
nitrogen7: allow 4 bit mode for winbond qspi chip
nitrogen7: add qspi-MX25L6405D
nitrogen7: swap GPIO1_IO02/GPIO1_IO03, only CLK02 can be slow clock
nitrogen7: add CONFIG_SPI_FLASH_SPANSION
nitrogen7_defconfig: add CONFIG_SPI_FLASH_MACRONIX
nitrogen7_qspi_defconfig: remove unneeded config
qspi-sst25vf016: minor changes, such as sflash_B1_size now 0
qspi-SST25VF016B: rename, increase to 76 Mhz
nitrogen7: nitrogen7_defconfig add CONFIG_BLOCK_CACHE
nitrogen7: use common code for eth init
nitrogen7: eth.c now in common directory
nitrogen7: move misc_init_r/do_kbd to common
nitrogen7: move mmc_init/ dram_init/ overwrite_console/ common_board_init/ splash_screen_prepare/ board_cfb_skip to common
nitrogen7: add display support
nitrogen7: add  CONFIG_SPI_FLASH_GIGADEVICE: to defconfigs
nitrogen7: add comment for ddr
nitrogen7: port to v2018.07

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

nitrogen7: allow environment import and export
nitrogen7: boot in secure mode
nitrogen7: add initial m4 support for FreeRTOS
nitrogen7: add secure boot option
nitrogen7: update to v2017.01
nitrogen7: update to v2017.03
nitrogen7: qspi: rename parameters file in lower case
nitrogen7: fix configuration by removing CONFIG_STACKSIZE
nitrogen7: fix I2C init

nitrogen7: fix m4 variables to match new naming convention

Previous variables were relying on 'bootdevs' which doesn't exist any
longer. Also the SYS_AUXCORE were still named CONFIG_SYS_AUXCCORE which
is now forbidden. Finally, sort the variables alphabetically.

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>