dt-bindings: hwmon/pmbus: Add ti,ucd90320 power sequencer

Document the UCD90320 device tree binding.

Signed-off-by: Jim Wright <wrightj@linux.vnet.ibm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20191205232411.21492-2-wrightj@linux.vnet.ibm.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>