net: dsa: mv88e6xxx: Fix releasing for the global2 interrupts

It is not possible to use devm_request_threaded_irq() because we have
two stacked interrupt controllers in one device. The lower interrupt
controller cannot be removed until the upper is fully removed. This
happens too late with the devm API, resulting in error messages about
removing a domain while there is still an active interrupt. Swap to
using request_threaded_irq() and manage the release of the interrupt
manually.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>