Add DAPM/ASoC helpers to create SDCA drivers

Add DAPM/ASoC helpers to create SDCA drivers

Merge series from Charles Keepax <ckeepax@opensource.cirrus.com>:

Add helper functions to add DAPM widgets, routes, ALSA controls,
and DAI drivers, these will be used to create SDCA function device
drivers.

This series should provide most of the core functionality needed to
get a device registered and have a working DAPM graph within the
device. There are some features that still need additional work, these
are marked with FIXMEs in the code. The two main things are SDCA
Clock Muxes (not used in our devices and needs some ASoC core work),
and better support for more complex SDCA volume control definitions
(our parts have fairly simple volumes, and SDCA has a large amount of
flexibility in how the volume control is specified).

The next steps in the process are to add helpers for the DAI ops
themselves, some IRQ handling, and firmware download. And finally we
should be able to actually add the SDCA class driver itself.