x86: apic - unify __setup_APIC_LVTT

To be able to unify this function we RE-introduce
APIC_DIVISOR for 64bit mode. This snipped was eliminated
in some time ago in a sake of clenup but now we need it
again since it allow up to get rid of #ifdef(s).

And lapic_is_integrated call is added in apic_64.c but
since we always have APIC integrated on 64bit cpu compiler
will ignore this call.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>