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/am335x_baltos_defconfig b/configs/am335x_baltos_defconfig
index 35a9a1b..5ff327b 100644
--- a/configs/am335x_baltos_defconfig
+++ b/configs/am335x_baltos_defconfig
@@ -8,7 +8,6 @@
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
-CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_SPL_FAT_SUPPORT=y
 CONFIG_FIT_VERBOSE=y
@@ -48,6 +47,7 @@
 CONFIG_ISO_PARTITION=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_NAND=y
+CONFIG_NAND_OMAP_GPMC_PREFETCH=y
 CONFIG_PHYLIB=y
 CONFIG_SYS_NS16550=y
 CONFIG_OMAP3_SPI=y