Some drivers use disable_irq / enable_irq and do the work
clearing the source in another thread instead of using a threaded
interrupt handler.

The irqchip used not having irq_disable and irq_enable
callbacks in this case, will lead to unnecessary spurious
interrupts:

On a disable_irq in a chip without a handler for this, the irq
core will remember the disable, but not actually call into the
irqchip. With a level triggered interrupt (where the source has
not been cleared) this will lead to an immediate retrigger, at
which point the irq-core will mask the irq. So having an
irq_disable callback in the irqchip will save us the interrupt
firing a 2nd time for nothing.

Drivers using disable / enable_irq like this, will call
enable_irq when they finally have cleared the interrupt source,
without an enable_irq callback, this will turn into an unmask,
at which point the irq will trigger immediately because when it
was originally acked the level was still high, so the ack was
a nop.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>