eth: fbnic: report FW uptime in health diagnose

eth: fbnic: report FW uptime in health diagnose

FW crashes are detected based on uptime going back, expose the uptime
via devlink health diagnose.

 $ devlink -j health diagnose pci/0000:01:00.0 reporter fw
 {"last_heartbeat":{"fw_uptime":{"sec":201,"msec":76}}}
 $ devlink -j health diagnose pci/0000:01:00.0 reporter fw
 last_heartbeat:
    fw_uptime:
      sec: 201 msec: 76

Reviewed-by: Lee Trager <lee@trager.us>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250916231420.1693955-9-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>