tests gpio_basic_api: Enable for nrf54l15bsim

Enable this test, and provide overlays, in the nrf54l15bsim

Note this test specs 2 GPIO pins to be shorted. This can be done
for the simulation target by calling zephyr.exe with the option
`-gpio_conf_file=shorts_config.txt`
Where  that file would contain this one line (for the provided overlay)
---- shorts_config.txt
short 1.1 1.2
----

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>