phy: add support for ET1011C phys

Adds an ET1011C PHY driver which is derived from the
Linux kernel PHY driver (drivers/net/phy/et1011c.c)
from the v3.9-rc2 tag. Note that an errata workaround
config option is implemented to allow for TX_CLK to be
enabled even when gigabit mode is negotiated. This
workaround is used on the PG1.0 TI814X EVM.

Signed-off-by: Matt Porter <mporter@ti.com>
Reviewed-by: Tom Rini <trini@ti.com>