fbdev: sh_mobile_hdmi: support hot-plugging of different HDMI / DVI displays

With this patch hot-plugging of an HDMI or a DVI monitor can select a different
video mode and reconfigure the LCDC and HDMI controllers accordingly. Due to a
lack of a standard API to inform framebuffer users of a changed video mode, the
framebuffer configuration is preserved regardless of a specific mode, selected
for the monitor. As described in a previous patch, this leads to smaller
framebuffers being displayed on larger monitors or a part of a larger
framebuffer being displayed on a smaller resolution monitor.

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