Input: ads7846 - handle HSYNC GPIO

Add handling of HSYNC signal emitted by the TI ADS7846 if it is hooked
up to a GPIO.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240430-gpio-leds-miscarm-v1-3-9c94d7711f6c@linaro.org


[dtor: dropped Spitz changes, kept platform data wait_for_sync option]
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>