drm/amd/display: fix gcc set but not used warning of variable 'old_plane_state'

define a new macro for_each_new_plane_in_state_reverse to replace
for_each_oldnew_plane_in_state_reverse, so that the unused variable
'old_plane_state' can be removed.

Fix gcc warning:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:10066:26: warning:
 variable ‘old_plane_state’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>