ARM: switch to use the generic show_mem() implementation

Switch ARM to use the generic show_mem() implementation, which displays
the statistics from the mm zone rather than walking the page arrays.

Acked-by: Mel Gorman &lt;mgorman <mgorman@suse.de>
Tested-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>