x86: apic - unify init_bsp_APIC

- remove redundant read of APIC_LVR register in 64bit mode
- APIC is always integrated for 64bit mode so
  gcc will eliminate lapic_is_integrated call

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>