x86, UV: Fix kdump reboot

After a crash dump on an SGI Altix UV system the crash kernel
fails to cause a reboot.  EFI mode is disabled in the kdump
kernel, so only the reboot_type of BOOT_ACPI works.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Cc: rja@sgi.com
LKML-Reference: <E1Q5Iuo-00013b-UK@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>