irqchip/stm32: Retrigger both in eoi and unmask callbacks

Sampling the IRQ line state in EOI and retriggering the interrupt to
work around missing level-triggered interrupt support only works for
non-threaded interrupts. Threaded interrupts must be retriggered the
same way in unmask callback.

Signed-off-by: Marek Vasut <marex@denx.de>
[maz: fixed missing static attribute]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200323235132.530550-1-marex@denx.de