drm/amd/display: Allocate DCN32/1 dmub memory to GTT

drm/amd/display: Allocate DCN32/1 dmub memory to GTT

[Why]
On DCN32/321  sometimes DMCUB takes a long time to flush.
This adds a delay before the data is available on the driver side even
after driver receives notification from DMCUB via inbox

[How]
Allocating DMUB memory to GTT gives much better latency. Limit this to
DCN32/1 for now; it will be made general to all other dGPUs later.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Sun peng (Leo) Li <sunpeng.li@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>