With a USB hub disconnected, devctl can be 0x19 for about a second
on am335x and will stay forever on at least omap3. And we get no
further interrupts when devctl session bit clears. This keeps
PM runtime active.

Let's fix the issue by polling devctl until the session bit clears
or times out. We can do this by making musb->irq_work into
delayed_work.

And with the polling implemented, we can now also have the quirk
for invalid VBUS it to avoid disconnecting too early while VBUS
is ramping up.

Fixes: 467d5c98 ("usb: musb: Implement session bit based runtime
PM for musb-core")
Fixes: 65b3f50e ("usb: musb: Add PM runtime support for MUSB DSPS
Tested-by: NLadislav Michl <ladis@linux-mips.org>
Tested-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NBin Liu <b-liu@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>