Revert "drm/amd/display: disable SubVP + DRR to prevent underflow"

This reverts commit 80c6d680.
The orignal commit was intended as a workaround to prevent underflow and
flickering when using one normal monitor and the other high refresh rate
monitor (> 120Hz).

This patch is being reverted in favour of a software solution to enable
SubVP+DRR

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>