drm/amdgpu: put MQDs in VRAM

Reduces preemption latency.
Only enable this for gfx10 and 11 for now
to avoid changing behavior on gfx 8 and 9.

v2: move MES MQDs into VRAM as well (YuBiao)
v3: enable on gfx10, 11 only (Alex)
v4: minor style changes, document why gfx10/11 only (Alex)

Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>