ARM: dts: ux500: Add touchscreen to the Skomer

This adds touchscreen support to the Ux500 Samsung
GT-S7710 "Skomer" mobile phone.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20200516212913.485365-1-linus.walleij@linaro.org