usb: cdns3: Fix deadlock when using NCM gadget

commit a1059896f2bfdcebcdc7153c3be2307ea319501f upstream.

The cdns3 driver has the same NCM deadlock as fixed in cdnsp by commit
58f2fcb3a845 ("usb: cdnsp: Fix deadlock issue during using NCM gadget").

Under PREEMPT_RT the deadlock can be readily triggered by heavy network
traffic, for example using "iperf --bidir" over NCM ethernet link.

The deadlock occurs because the threaded interrupt handler gets
preempted by a softirq, but both are protected by the same spinlock.
Prevent deadlock by disabling softirq during threaded irq handler.

Cc: stable <stable@kernel.org>
Fixes: 7733f6c3 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Acked-by: Peter Chen <peter.chen@kernel.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250318-rfs-cdns3-deadlock-v2-1-bfd9cfcee732@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>