pxa/spitz: Setup I2S pins for pxa2xx-i2s

The spitz has a WM8750 codec connected as I2S slave but doesn't use the
PXA I2S system clock.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Acked-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>