selftests/hid: import base_gamepad.py from hid-tools

We need to slightly change base_device.py for supporting HID-BPF,
so instead of monkey patching, let's just embed it in the kernel tree.

Link: https://lore.kernel.org/r/20240410-bpf_sources-v1-16-a8bf16033ef8@kernel.org
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>