tools/mtd-utils: add mirror md5sum

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r43760

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@43763 3c298f89-4303-0410-b956-a3cf2f4a3e73
ubi-utils: add mirror md5sum

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r43761

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@43764 3c298f89-4303-0410-b956-a3cf2f4a3e73