i2c: Add device tree support to i2c-pnx.c

This patch adds device tree support to the pnx-i2c driver by using platform
resources for memory region and irq and removing dependency on mach includes.

The following platforms are affected:

* PNX
* LPC31xx (WIP)
* LPC32xx

The patch is based on a patch by Jon Smirl, working on lpc31xx integration

Signed-off-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>