UPSTREAM: usb: dwc2: gadget: Prevent handling of host interrupts

UPSTREAM: usb: dwc2: gadget: Prevent handling of host interrupts

In host slave mode, the core asserts the rxready, txfifoempty interrupts
that get serviced in the gadget irq handler. Prevent servicing of these
when not in the gadget mode of operation.

Change-Id: I821c48399f876de045649507435bf2a3e9cf4cc5
Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Huang, Tao <huangtao@rock-chips.com>
(cherry picked from commit ee3de8d750134703c702534173cd8623d1b32c38)