drm/amd/display: Make DML2.1 P-State method force per stream

drm/amd/display: Make DML2.1 P-State method force per stream

[WHY & HOW]
Currently the force only works for a single display, make it so it can
be forced per stream.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>