usb: gadget: add hnp_polling_support and host_request_flag in usb_gadget

Add 2 flags for USB OTG HNP polling, hnp_polling_support is to indicate
if the gadget can support HNP polling, host_request_flag is used for
gadget to store host request information from application, which can be
used to respond to HNP polling from host.

Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>