Move request_irq() to an internal function which serves request_irq()
and the newly added request_threaded_irq() and devm_request_threaded_irq().
Likewise factor out parts of free_irq() to also be used with
devm_free_irq(). Add the storage and call to a thread_handler in case
of IRQ_WAKE_THREAD.
This is needed for the iwlwifi driver.
Sponsored by: The FreeBSD Foundation
MFC after: 10 days
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D30549
d16b6cb178