drm/amd/display/dc: add support for oem i2c in atom_firmware_info_v3_1

drm/amd/display/dc: add support for oem i2c in atom_firmware_info_v3_1

The fields are marked as reserved in atom_firmware_info_v3_1,
but thet contain valid data in all of the vbios images I've
looked at so add parse these fields as per
atom_firmware_info_v3_2.  The offsets are the same and the
reset of the structure is the same.

v2: squash in NULL checks

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>