mtd: nand: Introduce CONFIG_SYS_NAND_BUSWIDTH_16BIT

Introduce CONFIG_SYS_NAND_BUSWIDTH_16BIT option so that other NAND controller
drivers could use it when a 16-bit NAND is deployed.

drivers/mtd/nand/ndfc has CONFIG_SYS_NDFC_16BIT, so just rename it, so that
other NAND drivers could reuse the same symbol.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Reviewed-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
diff --git a/drivers/mtd/nand/ndfc.c b/drivers/mtd/nand/ndfc.c
index 6ebbb5e..213d2c9 100644
--- a/drivers/mtd/nand/ndfc.c
+++ b/drivers/mtd/nand/ndfc.c
@@ -156,7 +156,7 @@
 
 	struct nand_chip *chip = mtd->priv;
 
-#ifdef CONFIG_SYS_NDFC_16BIT
+#ifdef CONFIG_SYS_NAND_BUSWIDTH_16BIT
 	return (uint8_t) readw(chip->IO_ADDR_R);
 #else
 	return readb(chip->IO_ADDR_R);
@@ -218,7 +218,7 @@
 	nand->ecc.bytes = 3;
 	nand->select_chip = ndfc_select_chip;
 
-#ifdef CONFIG_SYS_NDFC_16BIT
+#ifdef CONFIG_SYS_NAND_BUSWIDTH_16BIT
 	nand->options |= NAND_BUSWIDTH_16;
 #endif