ARM: mxs: Simplify detection of CrystalFontz boards

As all CrystalFontz boards are compatible with "crystalfontz,cfa10036", make it
easier to add future boards.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>