Kconfig: define MD5 dependency for FIT support

FIT images require MD5 support to verify image checksums. So far this
was expressed by defining a CPP symbol in image.h. Since MD5 is now a
first class Kconfig citizen, express that in Kconfig instead.
Signed-off-by: NAndre Przywara <andre.przywara@arm.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

Kconfig

@@ -144,6 +144,7 @@ menu "Boot images"
 
 config FIT
 	bool "Support Flattened Image Tree"
+	select MD5
 	help
 	  This option allows you to boot the new uImage structure,
 	  Flattened Image Tree.  FIT is formally a FDT, which can include

include/image.h

@@ -67,7 +67,6 @@ struct lmb;
 #  endif
 # else
 #  define CONFIG_CRC32		/* FIT images need CRC32 support */
-#  define CONFIG_MD5		/* and MD5 */
 #  define CONFIG_SHA1		/* and SHA1 */
 #  define CONFIG_SHA256		/* and SHA256 */
 #  define IMAGE_ENABLE_CRC32	1