drm/amd/display: Introduce overlay cursor mode

[Why]

DCN is the display hardware for amdgpu. DRM planes are backed by DCN
hardware pipes, which carry pixel data from one end (memory), to the
other (output encoder).

Each DCN pipe has the ability to blend in a cursor early on in the
pipeline. In other words, there are no dedicated cursor planes in DCN,
which makes cursor behavior somewhat unintuitive for compositors.

For example, if the cursor is in RGB format, but the top-most DRM plane
is in YUV format, DCN will not be able to blend them. Because of this,
amdgpu_dm rejects all configurations where a cursor needs to be enabled
on top of a YUV formatted plane.

From a compositor's perspective, when computing an allocation for
hardware plane offloading, this cursor-on-yuv configuration result in an
atomic test failure. Since the failure reason is not obvious at all,
compositors will likely fall back to full rendering, which is not ideal.

Instead, amdgpu_dm can try to accommodate the cursor-on-yuv
configuration by opportunistically reserving a separate DCN pipe just
for the cursor. We can refer to this as "overlay cursor mode". It is
contrasted with "native cursor mode", where the native DCN per-pipe
cursor is used.

[How]

On each crtc, compute whether the cursor plane should be enabled in
overlay mode. If it is, mark the CRTC as requesting overlay cursor mode.

Overlay cursor should be enabled whenever there exists a underlying
plane that has YUV format, or is scaled differently than the cursor. It
should also be enabled if there is no underlying plane, or if underlying
planes do not cover the entire CRTC.

During DC validation, attempt to enable a separate DCN pipe for the
cursor if it's in overlay mode. If that fails, or if no overlay mode is
requested, then fallback to native mode.

v2:
* Update commit message for when overlay cursor should be enabled
* Also consider scale and no-underlying-plane case (cursor on crtc bg)
* Consider all underlying planes when determinig overlay/native, not
  just the plane immediately beneath the cursor, as it may not cover the
  entire CRTC.
* Fix typo s/decending/descending/
* Force native cursor on pre-DCN hardware

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>