base-files: gpio switch: check if direction can be set

Obviously not all GPIO controller allow to change the direction. The issue
is around since the beginning of the script but only due to the recent
changes error messages are more visible.

Add a check if a change of the direction is supported by the GPIO
controller and fallback to setting only the value if not.

Fixes: FS#1271
Signed-off-by: Mathias Kresin <dev@kresin.me>