drm/amd/display: Add functionality to get XGMI SS info

drm/amd/display: Add functionality to get XGMI SS info

[Why]
When XGMI is enabled, the DP reference clock needs to be adjusted
according to the XGMI spread spectrum percentage and mode. But first,
we need the ability to fetch this info.

[How]
Within the BIOS parser, Read from vBIOS when XGMI SS info is requested.

In addition, diags build uses include_legacy/atomfirmware.h for the
smu_info_v3_3 table headers. Update that as well.

Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>