usb: gadget: renesas_usbhs: unified callback function

renesas_usbhs needs callback for notify hotplug.
but it were 2 methods which are almost same.
This patch unified these into one.

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