Build only minimal images for Armhf

Build only the minimal image type for Armhf `uboot` and
`mx6qsabrelite` boards. While we have no support of graphical
stack for public version of boards above there is no sense to
create other image types for them.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

Differential Revision: https://phabricator.apertis.org/D7886