phy: Add support for SMSC LAN87xx PHYs

This adds support for the SMSC LAN87xx PHYs.

Following PHYs can be used by set CONFIG_PHY_SMSC to config.
 - SMSC LAN8700
 - SMSC LAN8710/LAN8720
 - SMSC LAN8710/LAN8720

A setup of PHY was copied from linux kenrel.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Fixed white space errors; modified commit message a bit.
Signed-off-by: Wolfgang Denk <wd@denx.de>