regulator: arizona: Update device tree binding to support Madera CODECs

The Arizona regulator drivers are now also used by the Cirrus Logic
Madera audio CODECs, update the binding document to link to the primary
binding document for these as well as the existing Arizona document.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>