[ARM] 3239/1: Add ARM optimised swab32

Patch from Andre McCurdy

Replaces generic swab32 routine with a more ARM friendly version.
Reduces kernel text size by approx 1200 bytes when compiled with
3.4.4 and approx 2400 bytes with 4.0.2

Probably some performance benefit as well.

Signed-off-by: Andre McCurdy <armccurdy@yahoo.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>