drm/amdgpu: Add memory vendor information

For ASICs with GC v9.4.3, determine the vendor information from scratch
register.

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