ENGR00219501 - FEC : Enable puase frame flow

ENGR00219501 - FEC : Enable puase frame flow

ENET pause frame has two issues (ticket TKT116501):
1. RX status fifo full.
2. XOFF has higher priority than XON when both XOFF and
   XON have pending request.

Both of the issues can cause RX FIFO overruns when RX bandwidth
is over 120Mbps.

The issue has been fixed on Rigel TO1.1 and Arik TO1.2. Pause
frame has been enabled to avoid the overrun issue.

Signed-off-by: Fugang Duan  <B38611@freescale.com>