x86: change x86_64 sanity checks to match i386.

They are mostly inocuous. APIC_INTEGRATED will expand to 1,
check_phys_apicid_present is checking for the same thing it was before,
etc. But the code is identical to i386 now, and will allow us to
integrate it.

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