ARM: dts: ux500: samsung-golden: Add touchkey

Adds support for the back and menu keys on golden.

Signed-off-by: Nick Reitemeyer <nick.reitemeyer@web.de>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20200621193822.133683-2-nick.reitemeyer@web.de


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>