drm/amdgpu: Add query_ras_error_count for mmhub v1_8

Add query_ras_error_count callback for mmhub v1_8.
It will be used to query and log mmhub error count
and memory block.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>