dt-bindings: gpio: aspeed,sgpio: Specify gpio-line-names

Some devicetrees specify gpio-line-names in the sgpio node despite it
not being defined by the binding. It's a reasonable thing to do, so
define the property to squash warnings such as:

    arch/arm/boot/dts/aspeed/aspeed-bmc-vegman-rx20.dtb: sgpio@1e780200: 'gpio-line-names' does not match any of the regexes: 'pinctrl-[0-9]+'
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20240530-dt-warnings-gpio-sgpio-interrupt-cells-v2-1-912cd16e641f@codeconstruct.com.auSigned-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/aspeed,sgpio.yaml

@@ -33,6 +33,11 @@ properties:
 
   gpio-controller: true
 
+  # Each SGPIO is represented as a pair of input and output GPIOs
+  gpio-line-names:
+    minItems: 160
+    maxItems: 256
+
   '#gpio-cells':
     const: 2