MLK-11132 usb: chipidea: otg: delay suspend for a_wait_vfall

MLK-11132 usb: chipidea: otg: delay suspend for a_wait_vfall

While A device as peripheral ends session by a_bus_drop, it will go
back to host role by transition to a_wait_vfall state, then ehci
host driver may access portsc status after controller enters suspend
, this will result in system hang since its clock is gated off.
This patch use existing autosuspend to delay the controller suspend
if it comes to a_wait_vfall state.

Signed-off-by: Li Jun <jun.li@freescale.com>
(cherry picked from commit b140fa6803ef6ececec17e435212a960a3169cc2)