phy: smsc: LAN8710/8720 are not Gbit PHYs

LAN8710/8720 are 10/100 Mbps PHYs, so fix the '.features' field.

Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>