drm/amd/display: Universal cursor plane hook-up.

Switch from legacy cursor to DRM cursor plane. Cursor
is not an actual plane but more of a subplane of each
pipe. Bind a DRM cursor plane instance to each CRTC.
Eliminate seperate FB object allocation for cursor and
clean  dm_crtc_cursor_set.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>