drm/bridge: dw-hdmi: add cec driver

Add a CEC driver for the dw-hdmi hardware.

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
[hans.verkuil: unsigned -> unsigned int]
[hans.verkuil: cec_transmit_done -> cec_transmit_attempt_done]
[hans.verkuil: add missing CEC_CAP_PASSTHROUGH]
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Tested-by: Hans Verkuil <hans.verkuil@cisco.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170802184108.7913-4-hverkuil@xs4all.nl