drm/tegra: Support ARGB and ABGR formats

These formats can easily be supported on all generations of Tegra.

Note that the XRGB and XBGR formats that we supported were in fact using
the ARGB and ABGR Tegra formats. This happened to work in cases where no
alpha was being considered. This change is also a fix for those formats.

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