drm: bridge: dw_hdmi: Audio: Add General Parallel Audio (GPA) driver

General Parallel Audio (GPA) interface is one of the supported
audio interface for synopsys HDMI module, which has verified for
i.MX8MPlus platform.
This is initial version for GPA.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Sandor Yu <Sandor.yu@nxp.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/f21ba3e8c4d9d028ac74c6f3c588ddbffe739399.1649989179.git.Sandor.yu@nxp.com