dt-bindings: mfd: rohm,bd71837-pmic: Add common properties

Add common properties appearing in DTSes (clock-names,
clock-output-names) with the common values (actually used in DTSes) to
fix dtbs_check warnings like:

arch/arm64/boot/dts/freescale/imx8mq-librem5-r2.dt.yaml:
pmic@4b: 'clock-names', 'clock-output-names', do not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Acked-By: Matti Vaittinen <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/rohm,bd71837-pmic.yaml

···
   clocks:
     maxItems: 1
 
+  clock-names:
+    const: osc
+
   "#clock-cells":
     const: 0
+
+  clock-output-names:
+    const: pmic_clk
 
 # The BD718x7 supports two different HW states as reset target states. States
 # are called as SNVS and READY. At READY state all the PMIC power outputs go