[ARM] pxa/csb726: switch to use smsc911x driver

csb726 used obsolete and not working out-of-tree driver smc911x.
Switch it to use new smsc911x driver.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Eric Miao <eric.miao@marvell.com>