drivers: introduce mtdblock abstraction

MTD block - abstraction over MTD subsystem, allowing
to read and write in blocks using BLK UCLASS.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
diff --git a/drivers/block/blk-uclass.c b/drivers/block/blk-uclass.c
index 512c952..9b8aa45 100644
--- a/drivers/block/blk-uclass.c
+++ b/drivers/block/blk-uclass.c
@@ -36,6 +36,7 @@
 	{ UCLASS_PVBLOCK, "pvblock" },
 	{ UCLASS_BLKMAP, "blkmap" },
 	{ UCLASS_RKMTD, "rkmtd" },
+	{ UCLASS_MTD, "mtd" },
 };
 
 static enum uclass_id uclass_name_to_iftype(const char *uclass_idname)