x86, mce: fix reporting of Thermal Monitoring mechanism enabled

Early Pentium M models use different method for enabling TM2
(per paragraph 13.5.2.3 of the "Intel 64 and IA-32 Architectures
Software Developer's Manual Volume 3A: System Programming Guide,
Part 1").

Tested on the affected Pentium M variant (model == 13).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>