intel_sst: add Master Volume

With this patch, Master Volume will control AUDIOLVOL(0x10c) and
AUDIORVOL(0x10d); while PCM Volume will control HPLVOL(0x123) and
HPRVOL(0x124).

Signed-off-by: Lu Guanqun <guanqun.lu@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>