HID: add documentation and Coccinelle script for FF registration race

HID drivers that rely on the HID core to register input devices must
ensure that all private data and capabilities (like force-feedback) are
fully initialized before registration.

When hid_hw_start() is called with HID_CONNECT_HIDINPUT, the input
device is registered immediately. This is racy if the driver attempts to
augment the input device in probe() after starting the hardware.

The correct way to handle this is to use the .input_configured()
callback.

Add documentation and a Coccinelle script to detect and prevent this
anti-pattern.

Assisted-by: Gemini:gemini-3.1-pro
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

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