drm/amdgpu: limit sdma instances to 2 for Arcturus in BU phase

Another 6 sdma instances do not work at present. Disable them to unblock KFD
for silicon bringup as a workaround
Signed-off-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1602,7 +1602,7 @@ 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;
+		adev->sdma.num_instances = 2;
 	else
 		adev->sdma.num_instances = 2;