HID: wiimote: Helper functions for synchronous requests

To initialize wiimote peripherals, the stream to the wiimote must be held
exclusively by the initializer, otherwise the initialization will fail. Many
initializations require multiple memory requests to be sent synchronously so we
need a way to lock the stream and release it when we are done.

This adds several helper functions which allow to lock the stream, then send
requests, wait for the answers and release the stream again.

When holding the lock, the function may sleep and interrupted by signals.
Also it returns after a short timeout so userspace shouldn't notice long
delays.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>