Add PCIE_SPEED_32_0GT and PCIE GEN5 support for amdgpu.

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>