dt-bindings: memory-controllers: ti,gpmc: add wait-pin polarity

The GPMC controller has the ability to configure the polarity for the
wait pin. The current properties do not allow this configuration.
This binding directly configures the WAITPIN<X>POLARITY bit
in the GPMC_CONFIG register by setting the "ti,wait-pin-polarity"
dt-property.

Signed-off-by: Benedikt Niedermayr <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Roger Quadros <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

Documentation/devicetree/bindings/memory-controllers/ti,gpmc-child.yaml

···
       Wait-pin used by client. Must be less than "gpmc,num-waitpins".
     $ref: /schemas/types.yaml#/definitions/uint32
 
+  ti,wait-pin-polarity:
+    description: |
+      Set the desired polarity for the selected wait pin.
+      0 for active low, 1 for active high.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [0, 1]
+
   gpmc,wait-on-read:
     description: Enables wait monitoring on reads.
     type: boolean