drm/amdgpu: Improve ras fatal error handling function

drm/amdgpu: Improve ras fatal error handling function

In multi-gpu case, a fatal error will generate several
fatal error interrupts. After improving this function,
the ras module can reuse this function to only
handle the first interrupt.

V3:
  Initialize event_id using RAS_EVENT_INVALID_ID.

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