ALSA: Add snd_pcm_direction_name() helper

Allow for retrieving string naming a direction of a stream without the
need of substream pointer.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20220511162403.3987658-2-cezary.rojewski@intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>