dt-bindings:trivial-devices: Add pli1209bc

Add trivial device entry for PLI1209BC Digital Supervisor from Vicor
Corporation.

Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/15a9fcfb5b9592c6d87f12c2a4c77fd069f5cfff.1645435888.git.sylv@sylv.io


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