phylib: add the ICPlus IP175C PHY driver

The ICPlus IP175C sports a 100Mbit/s 4-port switch in addition
to a dedicated 100Mbit/s WAN port.

Signed-off-by: Michael Barkowski <michael.barkowski@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>