x86: re-add reboot fixups

Jan Beulich noticed that the reboot fixups went missing during
reboot.c unification.

(commit 4d022e35)

Geode and a few other rare boards with special reboot quirks are
affected.

Reported-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>