usb: renesas_usbhs: add usbhsh_is_running()

It is possible to judge whether renesas_usbhs driver is running,
by checking attch irq mask.
This patch adds usbhsh_is_running() to check it.

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