imx6: reorganize build system

Changes include:

 * switching to profiles
 * adding ubifs support
 * building image for GW54XX board

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38441 3c298f89-4303-0410-b956-a3cf2f4a3e73
build: set owner root for all files on ubifs creation

When creating an image it makes no sense to have files owned by
the uid and gid on the host (and even creates a bug when for
example dropbear authorized_keys is included via env/files).

Signed-off-by: Joris de Vries <joris@apptrician.nl>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38442 3c298f89-4303-0410-b956-a3cf2f4a3e73