mrf24j40: change irq trigger type behaviour

This patch changes the irq trigger type value while calling
devm_request_irq by using IRQF_TRIGGER_LOW when no irq type was given.
Additional we add support for change the irq polarity while hw init if
high level or low level triggered irq type are given.

For rising edge triggered irq's the mrf24j40 can't deal with that, this
races at position of tx completion irq, while the irq is disabled we
readout the irq status registers. This will resets the irq line so other
irq's can occur. Wile readout the irq status register the irq is still
disabled and edge triggered interrupts will be ignored.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>