drivers: gpio: remove unused GPIO selection

Fixes: #38403

Removing unneeded `imply GPIO` and `CONFIG_GPIO=y` occurrences where no
files are added to the gpio zephyr library.

Also removed `CONFIG_GPIO=y` occurences where this is handled by
defconfigs for the soc or board.

Selection of GPIO without selecting any drivers results in the warning:

> No SOURCES given to Zephyr library: drivers__gpio
>
> Excluding target from build.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>