x86: apic - introduce imcr_ helpers

Impact: cleanup

Distinguish port writting magic into helpers with comments.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
LKML-Reference: <20090412165058.535921550@openvz.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>