drm/amdgpu: enable 8 SDMA instances for Arcturus

All the 8 SDMA instances work fine on the latest Gopher build model.
Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Snow Zhang <Snow.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c

@@ -1542,6 +1542,8 @@ static int sdma_v4_0_early_init(void *handle)
 
 	if (adev->asic_type == CHIP_RAVEN)
 		adev->sdma.num_instances = 1;
+	else if (adev->asic_type == CHIP_ARCTURUS)
+		adev->sdma.num_instances = 8;
 	else
 		adev->sdma.num_instances = 2;