amdgpu:support 16 ibs per submit for PAL/SRIOV

to support SRIOV and MCBP, need 16 IBs per submit

Signed-off-by: Qiang Yu <Qiang.Yu@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>