drm/amdgpu: Default disable GDS for compute VMIDs

The GDS and GWS blocks default to allowing all VMIDs to
access all entries. Graphics VMIDs can handle setting
these limits when the driver launches work. However,
compute workloads under HWS control don't go through the
kernel driver. Instead, HWS firmware should set these
limits when a process is put into a VMID slot.

Disable access to these devices by default by turning off
all mask bits (for OA) and setting BASE=SIZE=0 (for GDS
and GWS) for all compute VMIDs. If a process wants to use
these resources, they can request this from the HWS
firmware (when such capabilities are enabled). HWS will
then handle setting the base and limit for the process when
it is assigned to a VMID.

This will also prevent user kernels from getting 'stuck' in
GWS by accident if they write GWS-using code but HWS
firmware is not set up to handle GWS reset. Until HWS is
enabled to handle GWS properly, all GWS accesses will
MEM_VIOL fault the kernel.

v2: Move initialization outside of SRBM mutex

Signed-off-by: Joseph Greathouse <Joseph.Greathouse@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>