drm/bridge: tc358767: add GPIO & interrupt registers

Add GPIO and interrupt related registers for HPD work. Mark INTSTS_G and
GPIOI as volatile.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-23-tomi.valkeinen@ti.com