ARM: shmobile: r8a7740: add HDMI GPIO support

In order to enable HDMI GPIO selection from platform board,
this patch adds its interface to GPIO framework.

This patch is based on v1.0 manual

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>