drm/amdgpu: Enable gfx cache probing on HDP write for arcturus

This allows gfx cache to be probed and invalidated (for none-dirty cache lines)
on a HDP write (from either another GPU or CPU). This should work only for the
memory mapped as RW memory type newly added for arcturus, to achieve some cache
coherence b/t multiple memory clients.
Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Acked-by: Christian Konig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c

@@ -1194,6 +1194,9 @@ static int gmc_v9_0_hw_init(void *handle)
 		/* TODO for renoir */
 		mmhub_v1_0_update_power_gating(adev, true);
 		break;
+	case CHIP_ARCTURUS:
+		WREG32_FIELD15(HDP, 0, HDP_MMHUB_CNTL, HDP_MMHUB_GCC, 1);
+		break;
 	default:
 		break;
 	}