[ARM] 3029/1: Add HWUART support for PXA 255/26x

Patch from Matt Reimer

Adds support for HWUART on PXA 255 / 26x. This patch originally came from
http://svn.rungie.com/svn/gumstix-buildroot/trunk/sources/kernel-patches/000-gumstix-hwuart.patch


and has been tweaked by me.

Signed-off-by: Matt Reimer <mreimer@vpop.net>
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>