[WHY]
With some monitors when multi plane overlay is enabled the memory
clock switching mechanism has to change and, due to an error in the
initialization sequence, it may cause a black screen.

[HOW]
Change the firmware assisted memory clock switch initialization and
tear-down sequence utilizing the prepare_bandwidth and
optimize_bandwidth contexts.
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Felipe Clark <feclark@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>