net: emaclite: add barriers to support Xilinx Zynq platform

This patch adds barriers at appropriate places to ensure the driver
works on Xilinx Zynq ARM-based SoC platform.

Signed-off-by: Srikanth Thokala <sthokal@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>