dt-bindings: wkup-m3-ipc: Add firmware-name property

Document that the firmware-name property can be used to indicate a file
contains I2C sequences for PMIC voltage scaling during deep sleep.

Based on previous work by Russ Dill.
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
[dfustini: split from driver patch and convert to json-schema]
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220426200741.712842-2-dfustini@baylibre.com

Documentation/devicetree/bindings/soc/ti/wkup-m3-ipc.yaml

@@ -40,6 +40,12 @@ description: |+
   override the pin's existing bias (pull-up/pull-down) and value (high/low) when
   IO isolation is active.
 
+  Support for I2C PMIC Voltage Scaling
+  ====================================
+  It is possible to pass the name of a binary file to load into the CM3 memory.
+  The binary data is the I2C sequences for the CM3 to send out to the PMIC
+  during low power mode entry.
+
 properties:
   compatible:
     enum:
@@ -67,6 +73,10 @@ properties:
       mbox_wkupm3 child node.
     maxItems: 1
 
+  firmware-name:
+    description:
+      Name of binary file with I2C sequences for PMIC voltage scaling
+
   ti,vtt-gpio-pin:
     $ref: /schemas/types.yaml#/definitions/uint32
     description: GPIO pin connected to enable pin on VTT regulator
@@ -117,6 +127,7 @@ examples:
            ti,rproc = <&wkup_m3>;
            mboxes = <&am335x_mailbox &mbox_wkupm3>;
            ti,vtt-gpio-pin = <7>;
+           firmware-name = "am335x-evm-scale-data.bin";
         };
     };
 
@@ -157,6 +168,7 @@ examples:
            ti,rproc = <&wkup_m3>;
            mboxes = <&am437x_mailbox &mbox_wkupm3>;
            ti,set-io-isolation;
+           firmware-name = "am43x-evm-scale-data.bin";
         };
     };