tests: Add fp-device basic unit tests

Use the virtual image device as base for now, while the new setup allows
to create easily fake device drivers without including the driver in
libfprint itself and test all the fpi_device functionalities.

tests/meson.build

@@ -56,6 +56,7 @@ if 'virtual_image' in drivers
 
     unit_tests = [
         'fp-context',
+        'fp-device',
     ]
 
     foreach test_name: unit_tests