drm/amdgpu/gfx8: Enable interrupt on ME1_PIPE3

Otherwise FW cannot see the RLC ACK for the memory clean request
It's for Stoney.

Signed-off-by: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>