selftests/hid: move the gamepads definitions in the test file

More in line with the other test_* files.

No code change

Link: https://lore.kernel.org/r/20240410-bpf_sources-v1-17-a8bf16033ef8@kernel.org
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Author: Benjamin Tissoires