extcon: Perform device wakeup initialization upon driver probe

If USB cable is plugged in to usb port after system suspend,
system is not resuming. Fix the issue by attaching wakeup
source to device object which makes gpio vbus and id irq
wakeup capable upon system suspend.

Change-Id: I7436ad92ed37653e7db1deebde1a11e1c5165d6f
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>