Except on DaVinci, VBUS is now switched off as part of idling the
USB link (after a_wait_bcon) whenever a device is disconnected
from host. This is correct for OTG hosts, where either SRP or
an ID interrupt could turn VBUS on again.
However, for non-OTG hosts there's no way to turn VBUS on again,
so the host becomes unusable. And the procfs entry which once
allowed a manual workaround for this is now gone.
This patch adds an is_otg_enabled() check before scheduling the
switch-off timer in disconnect path, supporting a "classic host"
mode where SRP is unavailable.