Add SDCA DAI ops helpers

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

First, a couple of minor code fixups to already submitted code. Then
some patches to add new DAI ops helpers for the SDCA stuff, these allow
configuring things like the sample rate and finding out which SoundWire
port should be used for a specific SDCA streaming input/output terminal.
Still a few bits of outstanding work here (propogation of Cluster
information particularly) but his should be good enough to get some
basic use-cases working.

Hopefully we are getting fairly close to completing a first version of
the SDCA work now. Should be one more series to add FDL (firmware
downloading), then we should be able to send a first version of the
actual SDCA class driver itself.