lantiq: Sanitize device tree files

The device tree file of ARV752DPW uses numbers/hex values for gpio states and input event codes.

This cleans it up and uses the available macros from header files. This way the functions are easier to read and comprehend.

Signed-off-by: Andreas Eberlein <foodeas@aeberlein.de>
[sanitize all device tree files]
Signed-off-by: Mathias Kresin <dev@kresin.me>