dt-bindings: pinctrl: Add StarFive JH7100 bindings

Add bindings for the GPIO/pin controller on the JH7100 RISC-V SoC by
StarFive Ltd. This is a test chip for their upcoming JH7110 SoC.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>