fbdev: sh_mobile_hdmi: improve HDMI PHY parameters for high resolutions

High monitor resolutions also require higher clock frequencies, current HDMI
PHY parameters do not work well for resolutions higher than 720p.

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