gpio: lpc32xx: Use priv_data instead of platdata

The LPC32XX GPIO driver platdata currently contains GPIO state information,
which should go into priv_data. Thus rename lpc32xx_gpio_platdata to
lpc32xx_gpio_priv and convert to use dev_get_priv() instead.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Albert ARIBAUD <albert.aribaud@3adev.fr>