dt-bindings: ads7846: Add hsync-gpios

The TI ADS7846 emits a horizontal sync signal that is usually
connected to a GPIO for polling. Add a binding for this.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240430-gpio-leds-miscarm-v1-2-9c94d7711f6c@linaro.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>