[CPUFREQ] speedstep-centrino: Pentium 4 - M (HT) support

The Pentium 4 - Ms (HT) with CPUID 0xF34 and 0xF41 seem to support
centrino-like enhanced speedstep; however, no "table" support is possible.
Therefore, put NULL entries into speedstep-centrino.c

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Dave Jones <davej@redhat.com>