mtd: rawnand: Clarify Kconfig entry MTD_NAND

MTD_NAND is large and encloses much more than what the symbol is
actually used for: raw NAND. Clarify the symbol by naming it
MTD_RAW_NAND instead.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
diff --git a/arch/mips/configs/rbtx49xx_defconfig b/arch/mips/configs/rbtx49xx_defconfig
index 50a2c9a..96114ca 100644
--- a/arch/mips/configs/rbtx49xx_defconfig
+++ b/arch/mips/configs/rbtx49xx_defconfig
@@ -40,7 +40,7 @@
 CONFIG_MTD_COMPLEX_MAPPINGS=y
 CONFIG_MTD_PHYSMAP=y
 CONFIG_MTD_RBTX4939=y
-CONFIG_MTD_NAND=m
+CONFIG_MTD_RAW_NAND=m
 CONFIG_MTD_NAND_TXX9NDFMC=m
 CONFIG_BLK_DEV_LOOP=y
 CONFIG_BLK_DEV_RAM=y