ASoC: hdmi-codec: let the driver support HDMI sink

Devices like mobilephones, computers are typically used as
HDMI sources, but devices like TV, navigators will be HDMI
sinks.

for auto scenerios, In-Vehicle Infotainment(IVI) can be HDMI
sink to display movies from mobilephones.

Signed-off-by: Rongjun Ying <Rongjun.Ying@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Mark Brown <broonie@linaro.org>