x86/pat: Trivial: don't create debugfs for memtype if pat is disabled

If pat is disabled (boot with nopat), there's no need to create
debugfs for it, it's empty all the time.

Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1259236428-16329-1-git-send-email-dfeng@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>