drm/amdgpu: Add fatal error detected flag

For a RAS error that needs a full reset to recover, set the fatal error
status. Clear the status once the device is reset.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>