x86: mpparse: clean up code by introducing a few helper functions, fix

Impact: fix boot crash

This fixes commit a6830278.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1237403503.22438.21.camel@ht.satnam>
Signed-off-by: Ingo Molnar <mingo@elte.hu>