mtd: nand: add a helper to detect the nand type

This helper detects that whether the mtd's type is nand type.

Now, it's clear that the MTD_NANDFLASH stands for SLC nand only.
So use the mtd_type_is_nand() to replace the old check method
to do the nand type (include the SLC and MLC) check.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index f9bfe52..88409b8 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -354,6 +354,11 @@
 	return mtd->_read_oob && mtd->_write_oob;
 }
 
+static inline int mtd_type_is_nand(const struct mtd_info *mtd)
+{
+	return mtd->type == MTD_NANDFLASH || mtd->type == MTD_MLCNANDFLASH;
+}
+
 static inline int mtd_can_have_bb(const struct mtd_info *mtd)
 {
 	return !!mtd->_block_isbad;