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/common/Kconfig b/common/Kconfig
index 318d372..2bce8c9 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -599,9 +599,15 @@
 
 menu "Update support"
 
+config UPDATE_COMMON
+	bool
+	default n
+	select DFU_WRITE_ALT
+
 config UPDATE_TFTP
 	bool "Auto-update using fitImage via TFTP"
 	depends on FIT
+	select UPDATE_COMMON
 	help
 	  This option allows performing update of NOR with data in fitImage
 	  sent via TFTP boot.
@@ -616,6 +622,15 @@
 	default 100
 	depends on UPDATE_TFTP
 
+config UPDATE_FIT
+	bool "Firmware update using fitImage"
+	depends on FIT
+	depends on DFU
+	select UPDATE_COMMON
+	help
+	  This option allows performing update of DFU-capable storage with
+	  data in fitImage.
+
 config ANDROID_AB
 	bool "Android A/B updates"
 	default n