drm/tegra: dc: Implement hardware cursor on Tegra186 and later

The hardware cursor on Tegra186 differs slightly from the implementation
on older SoC generations. In particular the new implementation relies on
software for clipping the cursor against the screen. Fortunately, atomic
KMS already computes clipped coordinates for (cursor) planes, so this is
trivial to implement.

The format supported by the hardware cursor is also slightly different.

v2: use more drm_rect helpers (Dmitry)

Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>