ASoC: sn95031: make playback rails depend on actual pins they control

This patch makes the codec playback rails (headset and speaker) depend on
actual pins they control. This enables better power management of the codec

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Harsha Priya <priya.harsha@intel.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>