x86: provide bogus hard_smp_processor_id

We provide a bogus macro for x86_64 in case CONFIG_X86_LOCAL_APIC
is not set. It will always be set for x86_64, so the effect
is just to make the code equal to i386.

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