dt-bindings: Add MP2888 voltage regulator device

Monolithic Power Systems, Inc. (MPS) dual-loop, digital, multi-phase
controller.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210511055619.118104-4-vadimp@nvidia.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/trivial-devices.yaml

@@ -103,6 +103,8 @@ properties:
           - fsl,mpl3115
             # MPR121: Proximity Capacitive Touch Sensor Controller
           - fsl,mpr121
+            # Monolithic Power Systems Inc. multi-phase controller mp2888
+          - mps,mp2888
             # Monolithic Power Systems Inc. multi-phase controller mp2975
           - mps,mp2975
             # G751: Digital Temperature Sensor and Thermal Watchdog with Two-Wire Interface