ARM: spitz: Use software nodes for the ADS7846 touchscreen

ARM: spitz: Use software nodes for the ADS7846 touchscreen

Convert the Spitz to use software nodes to describe GPIOs for the
ADS7846 touchscreen. As part of the conversion switch from the custom
wait_for_sync() callback to defining hsync GPIO that can be used by
the ads7846 driver to detect hsync.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240628180852.1738922-11-dmitry.torokhov@gmail.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>