drm/amd/display: Fix RGB MPO underflow with multiple displays

[WHY]
With RGB MPO enabled, playing a video with multiple displays connected
results in underflow when closing the video window

[HOW]
Reverted the old change to fix this problem, which prevented pipe splits
for multiple display configurations and caused high MCLK speeds during
idle. Added a two step call to dc_update_planes_and_stream, first time
with pipe split disabled and the second time with pipe split enabled,
which fixed the underflow issue

Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Angus Wang <angus.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>