drm/amdgpu: Add function to add/remove gws to kfd process

GWS bo is shared between all kfd processes. Add function to add gws
to kfd process's bo list so gws can be evicted from and restored
for process.

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