drm/amd/display: Don't optimize bandwidth before disabling planes

[Why]
There is a window of time where we optimize bandwidth due to no streams
enabled will enable PSTATE changing but HUBPs are not disabled yet.
This results in underflow counter increasing in some hotplug scenarios.

[How]
Set the optimize-bandwidth flag for later processing once all the HUBPs
are properly disabled.

Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>