Convert CONFIG_NAND to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Sync up a few more, add imply's]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/db-mv784mp-gp_defconfig b/configs/db-mv784mp-gp_defconfig
index 1aeb2c5..567afef 100644
--- a/configs/db-mv784mp-gp_defconfig
+++ b/configs/db-mv784mp-gp_defconfig
@@ -39,6 +39,7 @@
 # CONFIG_SPL_PARTITION_UUIDS is not set
 CONFIG_SPL_OF_TRANSLATE=y
 # CONFIG_MMC is not set
+CONFIG_NAND=y
 CONFIG_NAND_PXA3XX=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_MACRONIX=y