drivers/extcon: Trigger gpio when device switch to usb host mode

Everytime device switch to usb host mode, trigger gpio to reset ethernet
bridge (LAN78xx), thus ethernet usb driver can be probed

Change-Id: I753c80cdcbf0a426738ce2bdcb44330bb2cabe71
Signed-off-by: Bo Zhang <bozhang@codeaurora.org>