net: stmmac: Terminate FPE workqueue in suspend

Add stmmac_fpe_stop_wq() in stmmac_suspend() to terminate FPE workqueue
during suspend. So, in suspend mode, there will be no FPE workqueue
available. Without this fix, new additional FPE workqueue will be created
in every suspend->resume cycle.

Fixes: 5a558611 ("net: stmmac: support FPE link partner hand-shaking procedure")
Signed-off-by: Mohammad Athari Bin Ismail <mohammad.athari.ismail@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>