usb: renesas_usbhs: add usbhs_pipe_attach() method

driver has to re-use the limited pipe for each device/endpoint
when it is USB host hub mode, since number of pipe has limitation.
This patch adds usbhsh_pipe_attach/detach() functions for it.
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>