drm/amdkfd: Set number of xgmi optimized SDMA engines for arcturus

some sdma engines are optimized for xgmi on arcturus.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Yong Zhao <Yong.Zhao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>