usb: renesas_usbhs: add a new callback for extcon notifier

To set host/peripheral mode by using extcon notifier, this patch
adds a new callback as "notifier" in renesas_usbhs_platform_callback.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>