x86: fix reboot problem with Dell Optiplex 745, 0KW626 board

we have seen a little problem in rebooting Dell Optiplex 745 with the
0KW626 board. Here is a small patch enabling reboot with this board,
which forces the default reboot path it into the BIOS reboot mode.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>