platform/x86: intel_pmc_core: Make debugfs entry for pch_ip_power_gating_status conditional

Check if the platform supports and only then add a debugfs entry for PCH
IP power gating status.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: David E. Box <david.e.box@intel.com>
Cc: Rajneesh Bhardwaj <irenic.rajneesh@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>