asoc: wcd9320: Use class AB headphone path for high-res formats

 * The class AB path is less efficient, but has a lower noise floor.
 * Enable this path for 24-bit or high (>96KHz) sample rate, as this
   tradeoff is worth it with lossless, high resolution music.

Change-Id: I0bf4e6f366e987f17d86b4e967e3bc8b40d86ed3