This commit adds support for the HDMI output on the Tegra20 SoC. Only
one such output is available, but it can be driven by either of the two
display controllers.

A lot of work on this patch has been contributed by NVIDIA's Mark Zhang
<markz@nvidia.com> and many other people at NVIDIA were very helpful in
getting the HDMI support and surrounding infrastructure to work.
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Mark Zhang <markz@nvidia.com>
Reviewed-by: Mark Zhang <markz@nvidia.com>
Tested-by: Mark Zhang <markz@nvidia.com>
Tested-and-acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>