common: update: add a generic interface for FIT image

The main purpose of this patch is to separate a generic interface for
updating firmware using DFU drivers from "auto-update" via tftp.

This function will also be used in implementing UEFI capsule update
in a later commit.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/image.h b/include/image.h
index 4094ee5..00bc03b 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1602,4 +1602,16 @@
 		.handler = _handler, \
 	}
 
+/**
+ * fit_update - update storage with FIT image
+ * @fit:        Pointer to FIT image
+ *
+ * Update firmware on storage using FIT image as input.
+ * The storage area to be update will be identified by the name
+ * in FIT and matching it to "dfu_alt_info" variable.
+ *
+ * Return:      0 on success, non-zero otherwise
+ */
+int fit_update(const void *fit);
+
 #endif	/* __IMAGE_H__ */