USB: EHCI: use otg_start_hnp() to intiate HNP in ehci-hub.c

EHCI core intiates HNP by calling otg_start_hnp() API when OTG port
is put into suspend to notify OTG driver which will take care of
HNP by suspending host and kicking gadget.

Change-Id: I2982b9f49140c2dcf2a32691e74f177e8d5d08cb
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>