drm/amdgpu: add raven gpu_info support

Add support for parsing the gpu info table on raven.
This is required to get the gpu config data for raven.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>