drm/amd/display: Stop leaking planes

[ Upstream commit 02680efb ]

[Why]
drm_plane_cleanup does not free the plane.

[How]
Call drm_primary_helper_destroy which will also free the plane.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>