ASoC: omap: Delete the obsolete omap-pcm

All DAI drivers are now using the new sdma-pcm platform driver. The
omap-pcm can be removed from the tree, but we need to keep the SND_OMAP_SOC
Kconfig option until the relevant defconfigs are updated to avoid
regression due to missing audio.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>