firmware-utils: made mkdir615h1 work for all Senao-produced devices as mksenaofw and cleaned up some of its formatting

Signed-off-by: Forest Crossman <cyrozap@gmail.com>

Backport of r41962

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@41984 3c298f89-4303-0410-b956-a3cf2f4a3e73