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

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

On some systems there could be bits set in the upper half of
the control value 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 failed on the IBM x3650 even though the ACPI
spec allows inequality.

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