drm/amdgpu: Rework retry fault removal

Rework retry fault removal from the software filter by
storing an expired timestamp for a fault that is being removed.
When a new fault comes, and it matches an entry in the sw filter,
it will be added as a new fault only when its timestamp is greater
than the timestamp expiry of the fault in the sw filter.
This helps in avoiding stale faults being added back into the
filter and preventing legitimate faults from being handled.

Suggested-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>