intel_sst: fix runtime pm issue

Use correct api for enabling/disabling runtime pm.  Additionally,
fix runtime suspend/resume to not duplicate pci core functions

Signed-off-by: Chandramouli Narayanan <chandramouli.narayanan@intel.com>
Tested-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>