ASoC: sst v2: Add mid platform driver

This patch adds the platform driver for mid asoc drivers.  This platfrom
driver sends commands to sst dsp engine driver for the dai operations.
For this purpose it depends on intel_sst driver which is currently in
staging tree

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>