mtd: Introduce mtd_block_isreserved()

In addition to mtd_block_isbad(), which checks if a block is bad or
reserved, it's needed to check if a block is reserved only (but not
bad). This commit adds an MTD interface for it, in a similar fashion to
mtd_block_isbad().

While here, fix mtd_block_isbad() so the out-of-bounds checking is done
before the callback check.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
[scottwood: Cherry-picked from Linux 8471bb73ba10ed67]
Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
index 18c32af..34b8ddc 100644
--- a/drivers/mtd/nand/nand_bbt.c
+++ b/drivers/mtd/nand/nand_bbt.c
@@ -1305,6 +1305,20 @@
 }
 
 /**
+ * nand_isreserved_bbt - [NAND Interface] Check if a block is reserved
+ * @mtd: MTD device structure
+ * @offs: offset in the device
+ */
+int nand_isreserved_bbt(struct mtd_info *mtd, loff_t offs)
+{
+	struct nand_chip *this = mtd->priv;
+	int block;
+
+	block = (int)(offs >> this->bbt_erase_shift);
+	return bbt_get_entry(this, block) == BBT_BLOCK_RESERVED;
+}
+
+/**
  * nand_isbad_bbt - [NAND Interface] Check if a block is bad
  * @mtd: MTD device structure
  * @offs: offset in the device