fbdev: sh-mobile_hdmi: remove un-necessity settings

Current gamut, acp, isrc1, isrc2 settings are wrong,
and not necessary for now.

Tested-by: Takanari Hayama <taki@igel.co.jp>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>