mtd: introduce mtd_can_have_bb helper

This patch introduces new 'mtd_can_have_bb()' helper function which checks
whether the flash can have bad eraseblocks. Then it changes all the
direct 'mtd->block_isbad' use cases with 'mtd_can_have_bb()'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/tests/mtd_speedtest.c b/drivers/mtd/tests/mtd_speedtest.c
index 4d2ed5c..2aec4f3 100644
--- a/drivers/mtd/tests/mtd_speedtest.c
+++ b/drivers/mtd/tests/mtd_speedtest.c
@@ -336,8 +336,7 @@
 		return -ENOMEM;
 	}
 
-	/* NOR flash does not implement block_isbad */
-	if (mtd->block_isbad == NULL)
+	if (!mtd_can_have_bb(mtd))
 		goto out;
 
 	printk(PRINT_PREF "scanning for bad eraseblocks\n");