IXP4xx family of network processors. The code still needs some
cleanup here and there, but it's to the point that it's should
be OK to push upstream.

Some of the remaining TODOs:

- Cleanup GPIO IRQ handling for edge-trigered HW (none exists ATM)
- Add IDE driver for various platforms
- Misc cleanups

This patch adds the changes to arch/arm/Makefile and arch/arm/Kconfig