powerpc: Use generic PHY driver for Marvell 88E1111 PHY on GE Fanuc SBC610

The Marvell PHY driver is currently being used for the 88E1111 on the
SBC610. This driver is causing the link to run in 10/Half mode, the generic
PHY driver is correctly configuring the PHY as 1000/Full.

Edit default config to use generic PHY driver.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>