bcm53xx: image: rework Makefile and merge some functions

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42644 3c298f89-4303-0410-b956-a3cf2f4a3e73
bcm53xx: image: document arguments of various functions

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42645 3c298f89-4303-0410-b956-a3cf2f4a3e73