usb: gadget: renesas_usbhs: add mod_host support

This is mod_host prototype support for renesas_usbhs driver.
It doesn't support USB-Hub, and USB-DMAC for now.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>