add new NAND config for i.MX6UL 14x14 EVK board, and disable USDHC2 when NAND enabled due to pin conflict.
Signed-off-by: Han Xu (cherry picked from commit 81e175bcc07792fab6010761daf6576bd600edda)
CONFIG_ARM=y CONFIG_ARCH_MX6=y CONFIG_TARGET_MX6UL_14X14_EVK=y CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6ul_14x14_evk/imximage.cfg,SYS_BOOT_NAND" CONFIG_CMD_GPIO=y CONFIG_CMD_DHCP=y CONFIG_CMD_PING=y