drm/amdgpu: Add interface to alloc gws from amdgpu

Add amdgpu_amdkfd interface to alloc and free gws
from amdgpu

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>