usb: renesas_usbhs: Add access control for INTSTS1 and INTENB1 register

INTSTS1 and INTENB1 register of renesas_usbhs can access only Host mode.
This adds process of accessing INTSTS1 and INTENB1 only when renesas_usbhs
is Host mode.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>