spi: fspi: Add power-domains to the DT bindings

i.MX8(X) based SoC use a power domain. Allow supplying this domain in
bindings.
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Han Xu <han.xu@nxp.com>
Link: https://lore.kernel.org/r/20230728060804.22796-1-alexander.stein@ew.tq-group.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-nxp-fspi.yaml

@@ -45,6 +45,9 @@ properties:
       - const: fspi_en
       - const: fspi
 
+  power-domains:
+    maxItems: 1
+
 required:
   - compatible
   - reg