Replace the old .txt binding with a new schema binding.
At the same time, some of the descriptions are updated to make them
clearer, fix errors, or just make them fit better into the style
of schema binding.

The cirrus,hs-bias-ramp-rate property was missing from the old .txt
binding and has been added to the yaml.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211028140902.11786-4-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>