samples/subsys/usb/hid-mouse: Convert to use the new GPIO API
samples/subsys/usb/hid-mouse: Convert to use the new GPIO API

Convert the sample to use the new GPIO API and additionally:
- add some error messages for unsuccessful GPIO API calls
- correct the index of `def_val` element used in the `right_button`
  callback, to match the one used when the callback is installed
- use flags defined in devicetree for the pin that drives the LED
  (for consistency, as this does not make much difference for a pin
  that is only toggled)

Signed-off-by: Andrzej Głąbek <6788b8d556a8a447102338fc996c42180ecff44e@nordicsemi.no>

nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr