Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c:282: warning: Function parameter or member 'vmhub' not described in 'gmc_v11_0_flush_gpu_tlb'
 drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c:282: warning: Function parameter or member 'flush_type' not described in 'gmc_v11_0_flush_gpu_tlb'
 drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c:322: warning: Function parameter or member 'flush_type' not described in 'gmc_v11_0_flush_gpu_tlb_pasid'
 drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c:322: warning: Function parameter or member 'all_hub' not described in 'gmc_v11_0_flush_gpu_tlb_pasid'

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>