dt-bindings: pinctrl: stm32: add new compatible for STM32MP135 SoC

New compatible to manage ball out and pin muxing of STM32MP135 SoC.

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210723132810.25728-2-alexandre.torgue@foss.st.com


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