dt-bindings: trivial-devices: Deprecate "ad,ad7414"

The correct vendor prefix for Analog Devices is "adi", not "ad". Both
forms are in use. Add the "adi,ad7414" version and deprecate the
"ad,ad7414" version.

Keep them together even though it breaks strict alphabetical ordering.

Link: https://lore.kernel.org/r/20240903-dt-trivial-devices-v1-2-ad684c754b9c@kernel.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>