dt-bindings: mmc: sdhci-pxa: Add minItems to pinctrl-names

Some older boards only require a default pinctrl. Add a minItems
property so these don't cause dt-validate warnings.

Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Duje Mihanović <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

Documentation/devicetree/bindings/mmc/sdhci-pxa.yaml

···
           items:
             - const: default
             - const: state_cmd_gpio
+          minItems: 1
 
         pinctrl-1:
           description:
···
           items:
             - const: default
             - const: state_uhs
+          minItems: 1
 
         pinctrl-1:
           description: