ASoC: Intel: Skylake: Add debugfs support

For debug, the kernel debugfs mechanism is available. We can add various
debug options for driver like module configuration read, firmware register
read etc.

This patch adds debugfs as a child to asoc plaform component and caller is
added for skylake driver to do init and cleanup of debugfs.

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Vunny Sodhi <vunnyx.sodhi@intel.com>
Signed-off-by: Guneshwor Singh <guneshwor.o.singh@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>