fbdev: sh_mobile_hdmi: add support for the "video=" kernel command line option

Add support for specifying video modes on the kernel command line. Mode
selection priorities are also changed such, that only exact matches of
specified modes with monitor modes from EDID are accepted, at least in width
and height. If none found - fall back to framebuffer default setting, if
available.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>