usb: core: use phy_exit during suspend if wake up is not supported

If the USB controller can wake up the system (which is the case for
example with the Mediatek USB3 IP) then we must not call phy_exit during
suspend to ensure that the USB controller doesn't have to re-enumerate
the devices during resume.
However, if the USB controller cannot wake up the system (which is the
case for example on various TI platforms using a dwc3 controller) then
we must call phy_exit during suspend. Otherwise the PHY driver keeps the
clocks enabled, which prevents the system from reaching the lowest power
levels in the suspend state.

Solve this by introducing two new functions in the PHY wrapper which are
dedicated to the suspend and resume handling.
If the controller can wake up the system the new usb_phy_roothub_suspend
function will simply call usb_phy_roothub_power_off. However, if wake up
is not supported by the controller it will also call
usb_phy_roothub_exit.
The also new usb_phy_roothub_resume function takes care of calling
usb_phy_roothub_init (if the controller can't wake up the system) in
addition to usb_phy_roothub_power_on.

Fixes: 07dbff0d ("usb: core: add a wrapper for the USB PHYs on the HCD")
Fixes: 178a0bce ("usb: core: hcd: integrate the PHY wrapper into the HCD core")
Reported-by: Roger Quadros <rogerq@ti.com>
Suggested-by: Roger Quadros <rogerq@ti.com>
Suggested-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>