mfd: Convert wm8350 physical I/O to regmap API

The driver still uses a custom cache implementation but the underlying
physical I/O is now done using the regmap API, saving some code and
avoiding allocating enormous scratch arrays on the stack.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>