usb: dwc3: gadget: Enable suspend events

commit d1d90dd2 upstream.

commit 72704f87 ("dwc3: gadget: Implement the suspend entry event
handler") introduced (nearly 5 years ago!) an interrupt handler for
U3/L1-L2 suspend events.  The problem is that these events aren't
currently enabled in the DEVTEN register so the handler is never
even invoked.  Fix this simply by enabling the corresponding bit
in dwc3_gadget_enable_irq() using the same revision check as found
in the handler.

Fixes: 72704f87

 ("dwc3: gadget: Implement the suspend entry event handler")
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210428090111.3370-1-jackp@codeaurora.org
[jackp@codeaurora.org: backport to pre-5.7 by replacing
 DWC3_IS_VER_PRIOR check with direct comparison of dwc->revision]
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>