[CPUFREQ] speedstep-centrino should ignore upper performance control bits

On some systems such as the IBM x3650 there are bits set in the
upper half of the control values provided by the _PSS object.
These bits are only relevant for cpufreq drivers that use IO ports
which are not currently supported by the speedstep-centrino driver.
The current MSR oriented code assumes that upper bits are not set
and thus fails to work correctly when they are.  e.g. the control
and status value equality check fails even though the ACPI spec
allows the inequality.

Signed-off-by: Gary Hade <garyh@us.ibm.com>
Signed-off-by: Dave Jones <davej@redhat.com>