kernel: allow specifying kernel images to be copied separately from kernel make command line

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43619 3c298f89-4303-0410-b956-a3cf2f4a3e73
mpc85xx: fix initramfs images

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43620 3c298f89-4303-0410-b956-a3cf2f4a3e73