drm/amdgpu: Add function parameter 'xcc_mask' not described in 'amdgpu_vm_flush_compute_tlb'

Fixes the below:

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c:1373: warning: Function parameter or member 'xcc_mask' not described in 'amdgpu_vm_flush_compute_tlb'

Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>