dt-bindings: mmc: spacemit,sdhci: add pinctrl support for voltage switching

Document pinctrl properties to support voltage-dependent pin
configuration switching for UHS-I SD card modes.

Add optional pinctrl-names property with two states:
- "default": For 3.3V operation with standard drive strength
- "state_uhs": For 1.8V operation with optimized drive strength

These pinctrl states allow the SDHCI driver to coordinate voltage
switching with pin configuration changes, ensuring proper signal
integrity during UHS-I mode transitions.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/spacemit,sdhci.yaml

@@ -44,6 +44,18 @@ properties:
       - const: axi
       - const: sdh
 
+  pinctrl-names:
+    minItems: 1
+    items:
+      - const: default
+      - const: uhs
+
+  pinctrl-0:
+    description: Default pinctrl state for 3.3V operation
+
+  pinctrl-1:
+    description: Optional pinctrl state for 1.8V UHS operation with "uhs" name
+
 required:
   - compatible
   - reg
@@ -62,4 +74,7 @@ examples:
       interrupt-parent = <&plic>;
       clocks = <&clk_apmu 10>, <&clk_apmu 13>;
       clock-names = "core", "io";
+      pinctrl-names = "default", "uhs";
+      pinctrl-0 = <&sdhci_default_cfg>;
+      pinctrl-1 = <&sdhci_uhs_cfg>;
     };