dt-bindings: rtc: pcf2127: Reference spi-peripheral-props.yaml

PCF2127 is an SPI device, thus its binding should reference
spi-peripheral-props.yaml.

Add a reference to spi-peripheral-props.yaml to fix the following
dt-schema warning:

imx7d-flex-concentrator.dtb: rtc@0: 'spi-max-frequency' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Fabio Estevam <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml

···
 
 allOf:
   - $ref: rtc.yaml#
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
 
 maintainers:
   - Alexandre Belloni <[e-mail]>
···
   - compatible
   - reg
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |