mtd: rename nand into rawnand in Kconfig prompt

Sync the Kconfig raw NAND entry title with the code architecture.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/Kconfig

@@ -1,6 +1,6 @@
 
 menuconfig NAND
-	bool "NAND Device Support"
+	bool "Raw NAND Device Support"
 if NAND
 
 config SYS_NAND_SELF_INIT