ASoC: da7213: Refactor sysclk(), pll() functions to improve handling

ASoC: da7213: Refactor sysclk(), pll() functions to improve handling

Currently the handling of the PLL in the driver is a little clunky,
and not ideal for all modes. This patch updates the code to make it
cleaner and more sensible for the various PLL states.

Key items of note are:
 - MCLK squaring is now handled directly as part of the sysclk()
   function, removing the need for a private flag to set this feature.
 - All PLL modes are defined as an enum, and are handled as a case
   statement in pll() function to clean up configuration. This also
   removes any need for a private flag for SRM.
 - For 32KHz mode, checks are made on codec master mode and correct
   MCLK rates, to avoid incorrect usage of PLL for this operation.
 - For 32KHz mode, SRM flag now correctly enabled and fout set to
   sensible value to achieve appropriate PLL dividers.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>