ARM: LPC32xx: Adjust device tree node to new standard num-cs

In spi-pl022.c, the new device tree binding is now "num-cs" for the number of
chip selects. Further, pl022,hierarchy and pl022,slave-tx-disable isn't
supported in favour of reasonable defaults in the driver.

Adjusting phy3250.dts to it.

Signed-off-by: Roland Stigge <stigge@antcom.de>