drm/amdgpu: Introduce funcs for populating CPER

Introduce utility functions designed to assist
in populating CPER records.

v2: call cper_init/fini in device_ip_init/fini.

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>