amd/display: check cursor plane matches underlying plane

The current logic checks whether the cursor plane blending
properties match the primary plane's. However that's wrong,
because the cursor is painted on all planes underneath. If
the cursor is over the primary plane and the overlay plane,
it's painted on both pipes.

Iterate over the CRTC planes and check their scaling match
the cursor's.

v4: fix typo in commit message (Harry)

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>