drm/bridge/sii8620: add remote control support

MHL specification defines Remote Control Protocol(RCP) to
send input events between MHL devices.
The driver now recognizes RCP messages and reacts to them
by reporting key events to input subsystem, allowing
a user to control a device using TV remote control.

Signed-off-by: Maciej Purski <m.purski@samsung.com>
Acked-by: Sean Young <sean@mess.org>
Acked-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1503565087-19730-1-git-send-email-m.purski@samsung.com