dt-bindings: clock: uniphier: Add clock binding for SoC-glue

Update binding document for clocks implemented in SoC-glue.

Signed-off-by: Kunihiko Hayashi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/clock/socionext,uniphier-clock.yaml

···
           - socionext,uniphier-ld20-peri-clock
           - socionext,uniphier-pxs3-peri-clock
           - socionext,uniphier-nx1-peri-clock
+      - description: SoC-glue clock
+        enum:
+          - socionext,uniphier-pro4-sg-clock
 
   "#clock-cells":
     const: 1