drm/nouveau/pm: detect when we need dll disabled for gddr3

Fixes minor flickering on NVS295 when at perflvl 0.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Martin Peres <martin.peres@labri.fr>

diff --cc drivers/gpu/drm/nouveau/nouveau_mem.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_perf.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_pm.h
Simple merge