env: ubi: support configurable VID offset

Introduce KConfig CONFIG_ENV_UBI_VID_OFFSET to allow providing custom
VID header offsets for the environment on UBI.

Signed-off-by: Hamish Guthrie <hamish.guthrie@kistler.com>
Signed-off-by: Markus Klotzbuecher <markus.klotzbuecher@kistler.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Cc: Kyungmin Park <kmpark@infradead.org>
diff --git a/env/Kconfig b/env/Kconfig
index 06ab4bc..d86a9bf 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -516,6 +516,13 @@
 	help
 	  Name of the redundant volume that you want to store the environment in.
 
+config ENV_UBI_VID_OFFSET
+	int "ubi environment VID offset"
+	depends on ENV_IS_IN_UBI
+	default 0
+	help
+	  UBI VID offset for environment. If 0, no custom VID offset is used.
+
 endif
 
 config USE_DEFAULT_ENV_FILE