Impact: Bug fix when CPU hotplug is disabled

Correct the following broken __cpuinit/__cpuexit annotations:

- mce_cpu_features() is called from mce_resume(), and so cannot be
  __cpuinit.
- mce_disable_cpu() and mce_reenable_cpu() are called from
  mce_cpu_callback(), and so cannot be __cpuexit().

Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>