Autosuspend sorta works on dwc2 but sometimes causes the device to be
reset.  In some cases this is intentional due to the "remote wakeup"
problem on the dwc2 host-only port (see the
"snps,need-phy-full-reset-on-wake" property) but in other cases it
looks like something about the suspend sequence in dwc2 and/or the PHY
isn't quite right.

In general Chrome OS doesn't use autosuspend much and it's turned off
for almost all USB devices.  Notably the only devices that have
autosuspend enabled are:
- webcams
- security keys
- usb peripherals that are expected to be connected internally
See power manager's "udev/gen_autosuspend_rules.py"

If we disable autosuspend then the main downside is that security keys
will take up more power.  That's not so good for laptops, but it's
unlikely to be a big negative for Chromeboxes.

We'll include this udev rule on any "ac_only" devices.  That will make
them work a little better with webcams in particular (one of the few
things you might plug in that had autosuspend turned on).  It's
unfortunate that we can't do something that would fix everyone with no
compromises, but this is better than nothing.  If nothing else it's
not really expected that someone would plug a webcam into their
laptop.

BUG=b:67983206
TEST=Logitech webcam enumerates more reliably

Change-Id: I0c29976ab8741003e936b23828fea6dc06e9cc11
Reviewed-on: https://chromium-review.googlesource.com/740579


Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Heng-ruey Hsu <henryhsu@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>