fbdev: sh_mobile_hdmi: 32bit register access support

Latest SuperH HDMI allows 32bit access only.
But the data is 8bit. So, we can keep compatibility by switching 8/32 bit access.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>