net: rmnet_usb: Enable wakeup from system suspend

The MDM device already supports sending remote wakeup signaling over
HSIC during normal bus auto-suspend. However, this feature is
explicitly suppressed when the kernel enters system-wide suspend.
This fix allows the device to continue to send resume signaling in
order to wake the kernel out of suspend.

Change-Id: I93d963ca56704e3011b55afe2646b0f3714ffdec
Signed-off-by: Jack Pham <jackp@codeaurora.org>