wl18xx: wlan_irq: support platform dependent interrupt types

* Interrupt request need to happen when the wilink chip is powered on and
  driving the wlan_irq line. This avoids spurious interrupt issues that
  are a result of different external pulls configuration on different
  platforms
* Allow working with wl18xx level-low and falling edge irqs by configuring
  wl18xx to invert the device interrupt

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>