dt-bindings: pinctrl: Add thead,th1520-pinctrl bindings

Add bindings for the pin controllers on the T-Head TH1520 RISC-V SoC.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Tested-by: Thomas Bonnefille <thomas.bonnefille@bootlin.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
[dfustini: add thead,pad-group to select the pin controller instance]
Signed-off-by: Drew Fustini <dfustini@tenstorrent.com>
Link: https://lore.kernel.org/20240930-th1520-pinctrl-v3-1-32cea2bdbecb@tenstorrent.com


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