[ARM] add_memory() build fix

This is back again.  Offending patch is x86_64-mm-hotadd-reserve.patch

arch/arm/kernel/setup.c:435: error: conflicting types for 'add_memory'
include/linux/memory_hotplug.h:102: error: previous declaration of 'add_memory' was here
arch/arm/kernel/setup.c:435: error: conflicting types for 'add_memory'
include/linux/memory_hotplug.h:102: error: previous declaration of 'add_memory' was here

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>