fjes: ethtool -d support for fjes driver

This patch adds implementation of supporting
ethtool -d for fjes driver. By using ethtool -d,
you can get registers dump of Exetnded socket device.

  # ethtool -d es0

Offset          Values
------          ------
0x0000:         01 00 00 00 08 00 00 00 00 00 00 00 00 00 00 00
0x0010:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0020:         02 00 00 80 02 00 00 80 64 a6 58 08 07 00 00 00
0x0030:         00 00 00 00 28 80 00 00 00 00 f9 e3 06 00 00 00
0x0040:         00 00 00 00 18 00 00 00 80 a4 58 08 07 00 00 00
0x0050:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0060:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0070:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0080:         00 00 00 00 00 00 e0 7f 00 00 01 00 00 00 01 00
0x0090:         00 00 00 00

Signed-off-by: Taku Izumi <izumi.taku@jp.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>