PCC: Disable compilation by default

PCC is made selectable only by clients which use it. e.g. CPPC
Default it to disabled so that it is not included accidentally on
platforms which dont use it.

Signed-off-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Reviewed-by: Al Stone <al.stone@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>