drm/amdgpu: Read PSPv13 OS version from register

PSP OS updates the version information in register. On APUs with PSPv13,
PSP OS will already be loaded with SBIOS. Hence use the version register
instead of using information in driver binary header.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>