ARM: 6116/1: kdump: reserve memory for crashkernel

Implemented ARM support for command line option
"crashkernel=size@start" which allows user to reserve some memory
for a dump capture kernel.

Signed-off-by: Mika Westerberg <ext-mika.1.westerberg@nokia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>