drm/amd/display: Allow planes on all crtcs

4.9 kernel will always add the assigned crtc to possible_crtcs on a
plane. This is no longer the case on newer kernels. Make sure we allow
any plane on any crtc.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>