imx6: minor image cleanup

Signed-off-by: Luka Perkov <luka@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38628 3c298f89-4303-0410-b956-a3cf2f4a3e73
kirkwood: extend image/Makefile

* use lower case letters in generated images
* extend support for boot/ directory
* fix some typos

Signed-off-by: Luka Perkov <luka@openwrt.org>
Signed-off-by: Felix Kaechele <heffer@fedoraproject.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38629 3c298f89-4303-0410-b956-a3cf2f4a3e73