drm/amdgpu: parse the gpu_info firmware (v4)

And populate the gfx structures from it.

v2: update the structures updated by the table
v3: rework based on new table structure
v4: simplify things

Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Tested-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>