x86, mce: print header/footer only once for multiple MCEs

When multiple MCEs are printed print the "HARDWARE ERROR" header
and "This is not a software error" footer only once. This
makes the output much more compact with many CPUs.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>