drm: bridge: add DesignWare HDMI I2S audio support

Current dw-hdmi is supporting sound via AHB bus, but it has
I2S audio feature too. This patch adds I2S audio support to dw-hdmi.
This HDMI I2S is supported by using ALSA SoC common HDMI encoder
driver.

Tested-by: Jose Abreu <joabreu@synopsys.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/8737j2bxba.wl%kuninori.morimoto.gx@renesas.com