pinctrl: pxa: pxa2xx: add pin configuration support

Add pin configuration for pxa2xx architectures. PXA doesn't provide any
bias, push, pull capabilities. The only capability is to set a state for
the pins when the platform enter sleep or deep sleep mode.

The state of a pin is set by :
 - whether the GPIO direction was input or output
 - if it is output, a register set programs whether the pin should be
   held to ground or VccIO

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>