ASoC: SOF: Intel: cnl: add pointer ops to use DPIB position

Add .pcm_pointer ops for cannonlake to read DPIB/posbuf and get pointer
for ALSA, to align with apollolake.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>