Interrupt transfers aren't meant to be used from the async list
(the EHCI spec indicates trouble with low/full-speed intr on async).

Build a periodic list instead, and provide an API to make use of it.
Then, use that API from the existing interrupt transfer API.

This provides support for USB keyboards using EHCI.

Use timeouts to ensure we cannot get stuck in the keyboard scanning
if something wrong happens (USB device unplugged or fatal I/O error)
Signed-off-by: NVincent Palatin <vpalatin@chromium.org>
Signed-off-by: NJulius Werner <jwerner@chromium.org>
Signed-off-by: NSimon Glass <sjg@chromium.org>