drm/tegra: hdmi: Enable audio over HDMI

In order to use the HDA codec to forward audio data to the HDMI codec it
needs the ELD that is parsed from the monitor's EDID.

Also implement an interoperability mechanism between the HDA controller
and the HDMI codec. This uses vendor-defined scratch registers to pass
data from the HDMI codec driver to the HDMI driver (that implements the
receiving end of the HDMI codec). A custom format is used to pass audio
sample rate and channel count to the HDMI driver.

Signed-off-by: Thierry Reding <treding@nvidia.com>