dt-bindings: pinctrl: rockchip: add rk3588

Add compatible string for rk3588 pin controller. No other changes
are required, since the new controller can use the old binding.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20220422170920.401914-12-sebastian.reichel@collabora.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>