x86: cpuinit-annotate SMP boot trampolines properly

Add missing annotations, and make use of include/linux/init.h's
macros.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4AA0E8F60200007800013703@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>