Add support for various boot devices like NAND, QSPINOR, SPINOR, eMMC, EIMNOR, SATA.
Modify board level files to support the feature and add corresponding defconfig files
Signed-off-by: Ye Li
CONFIG_ARM=y CONFIG_ARCH_MX6=y CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6slevk/imximage.cfg,MX6SL,SPLASH_SCREEN" CONFIG_TARGET_MX6SLEVK=y CONFIG_CMD_GPIO=y CONFIG_SPI_FLASH=y CONFIG_SPI_FLASH_STMICRO=y
