dt-bindings: clock: bcm63xx: add 6318 gated clock bindings

Add BCM6318 to the binding documentation for the gated clock controllers found
on BCM63xx SoCs.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20200610140858.207329-2-noltari@gmail.com


Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>