add 'miitool' command to view media-independent interface status ...

This command is based on the 'mii-diag' and 'mii-tool'
Unix utilities, but it lacks routines to manipulate
MII state (e.g. reset MII, restart autonegotiation
or force MII mode).

This version of the 'miitool' command has no GbE support,
but we can upgrade it in the future. The GbE support
patch for generic 'mii-tool' is here
http://ftp.debian.org/debian/pool/main/n/net-tools/net-tools_1.60-24.2.diff.gz

EXAMPLE:

barebox:/ miitool -vv /dev/phy0
negotiated 100baseTx-FD, link ok
  registers for MII PHY:
    3100 782d 0013 78e2 01e1 45e1 0007 2001
    0000 ffff ffff ffff ffff ffff ffff ffff
    0084 4780 0000 0000 0422 0000 0000 0000
    0000 0000 0080 0000 ffff 0000 0000 3660
  product info: Level One LXT971A rev 2
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>