drm/amd/display: Compare plane when looking for pipe split being lost

[Why]
There are situations where we go from 2 pipe to 1 pipe in MPO, but this
isn't a pipe split being lost -- it's a plane disappearing in (i.e. video overlay
goes away) so we lose one pipe. In these situations we don't want to
disable the pipe in a separate operation from the rest of the pipe
programming sequence. We only want to disable a pipe in a
separate operation when we're actually disabling pipe split.

[How]
Make sure the pipe being lost has the same stream AND plane
as the old top pipe to ensure.

Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>