firmware: cs_dsp: Allow creation of event controls

Some firmwares contain controls intended to convey firmware state back
to the host. Whilst more infrastructure will probably be needed for
these in time, as a first step allow creation of the controls, so said
firmwares arn't completely rejected.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20211117132300.1290-10-ckeepax@opensource.cirrus.com


Signed-off-by: Mark Brown <broonie@kernel.org>