fastboot: sparse: implement reserve()

In order to process the CHUNK_TYPE_DONT_CARE properly, there is
a requirement to be able to 'reserve' a specified number of blocks
in the storage media. Because of the special handling of "bad blocks"
in NAND devices, this is implemented in a storage abstraction function.

Signed-off-by: Steve Rae <srae@broadcom.com>
Reviewed-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/include/image-sparse.h b/include/image-sparse.h
index f6869d6..b0cc500 100644
--- a/include/image-sparse.h
+++ b/include/image-sparse.h
@@ -19,6 +19,10 @@
 				 lbaint_t blk,
 				 lbaint_t blkcnt,
 				 const void *buffer);
+
+	lbaint_t	(*reserve)(struct sparse_storage *info,
+				 lbaint_t blk,
+				 lbaint_t blkcnt);
 };
 
 static inline int is_sparse_image(void *buf)