drm/amdgpu: added support to get mGPU DRAM base

resolves issue with RAS error injection in mGPU configuration

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
5 files changed