dt-bindings: pinctrl: apple,pinctrl: Add apple,t6000-pinctrl compatible

This new SoC uses the same pinctrl hardware, so just add a new per-SoC
compatible.

Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>