x86: use APIC_INTEGRATED tests in x86_64

This patch does not change the behaviour of x86_64, since APIC_INTEGRATED
is always defined as (1). But the code now matches exactly i386 version
(well, this part of the code, at least)

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>