dt-bindings: regulator: pca9450: Add sd-vsel-gpios to read back LDO5 status

In order to know the current status (which of the two control
registers is used) for the LDO5 regulator, we need to route back the
USDHC_VSELECT signal by setting the SION bit in the IOMUX.

By adding the according GPIO as sd-vsel-gpios to the LDO5 node, we
allow the regulator driver to sample the current status of the
SD_VSEL signal that is used to select the correct control register.

The SD_VSEL on the PMIC is always an input. It's driven by the SoC's
VSELECT signal (controlled by the USDHC controller) and we use the
SION bit in the IOMUX to internally loop back the signal in order to
sample it using the GPIO.

As the SD_VSEL pin is directly routed to the LDO5 regulator in the
PMIC, make the sd-vsel-gpios property part of the LDO5 node.

SoC                                  PMIC
+-----------------------+           +-------------------+
|                       |           |                   |
|                       |           |                   |
|  GPIO <----------+    |           |                   |
|                  |    |    SD_VSEL|   +-------+       |
|  USDHC_VSELECT ->+------------------->| LDO5  |       |
|                       |           |   +-------+       |
|                       |           |                   |
+-----------------------+           +-------------------+

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
---
Changes for v2:
* extend commit message
* split into two patches (revert old sd-vsel-gpios seperately)

Documentation/devicetree/bindings/regulator/nxp,pca9450-regulator.yaml

@@ -41,8 +41,24 @@ properties:
     description: |
       list of regulators provided by this controller
 
+    properties:
+      LDO5:
+        type: object
+        $ref: regulator.yaml#
+        description:
+          Properties for single LDO5 regulator.
+
+        properties:
+          sd-vsel-gpios:
+            description:
+              GPIO that can be used to read the current status of the SD_VSEL
+              signal in order for the driver to know if LDO5CTRL_L or LDO5CTRL_H
+              is used by the hardware.
+
+        unevaluatedProperties: false
+
     patternProperties:
-      "^LDO[1-5]$":
+      "^LDO[1-4]$":
         type: object
         $ref: regulator.yaml#
         description: