Convert CONFIG_NAND_OMAP_GPMC et al and CONFIG_NAND_MXC to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND_MXC
   CONFIG_NAND_OMAP_GPMC
   CONFIG_NAND_OMAP_GPMC_PREFETCH
   CONFIG_NAND_OMAP_ELM
   CONFIG_SPL_NAND_AM33XX_BCH
   CONFIG_SPL_NAND_SIMPLE
   CONFIG_SYS_NAND_BUSWIDTH_16BIT

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
[trini: Finish migration of CONFIG_SPL_NAND_SIMPLE, fix some build issues,
        add CONFIG_NAND_MXC so we can do CONFIG_SYS_NAND_BUSWIDTH_16BIT]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx31pdk_defconfig b/configs/mx31pdk_defconfig
index 5282aa4..3fcc0c0 100644
--- a/configs/mx31pdk_defconfig
+++ b/configs/mx31pdk_defconfig
@@ -8,7 +8,6 @@
 CONFIG_BOOTDELAY=1
 CONFIG_SPL=y
 CONFIG_CMD_BOOTZ=y
-CONFIG_CMD_NAND=y
 CONFIG_CMD_SPI=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_DHCP=y
@@ -17,3 +16,5 @@
 CONFIG_CMD_DATE=y
 CONFIG_ENV_IS_IN_NAND=y
 # CONFIG_MMC is not set
+CONFIG_NAND=y
+CONFIG_NAND_MXC=y