x86: let intel 64-bit use intel.c

now that arch/x86/kernel/cpu/intel_64.c and
arch/x86/kernel/cpu/intel.c are equal, drop
arch/x86/kernel/cpu/intel_64.c and fix up
the glue.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>