ASoC: max98396: Some assorted fixes and additions

Merge series from Daniel Mack <daniel@zonque.org>:

This is a series of some patches that I collected while using the
max98396 driver is a TDM mode setup.

They correct BSEL and PCM mode configs, add support for power supplies
and add some bits to the documentation.

The code is tested in TDM-16 and TDM-8 mode with 32 channel width.