dt-bindings: pinctrl: eswin: Document for EIC7700 SoC

dt-bindings: pinctrl: eswin: Document for EIC7700 SoC

Add EIC7700 pinctrl device for all configurable pins.
For the EIC7700 pinctrl registers, each register (32 bits)
controls the characteristics of a single pin.
It supports setting function multiplexing, Schmitt trigger,
drive strength, pull-up/pull-down, and input enable.

Co-developed-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Yulin Lu <luyulin@eswincomputing.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/20250612104811.1206-1-luyulin@eswincomputing.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>