ASoC: mfld_machine: make use of soc_register_card API

This patch removes the old method of soc-audio device creation in mfld machine
and makes use of new soc_register_card API to register the card

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>