drm/amdgpu: Use vbios table for gpu info on vega20

Use the vbios table rather than gpu info firmware.

Squash of the following patches:
drm/amdgpu/vg20: fallback to vbios table if gpu info fw is not available (v2)
drm/amdgpu: drop gpu_info firmware for vega20

Reviewed-by: Amber Lin <Amber.Lin@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>