intc/xilinx_intc: Handle level interrupt retriggering

intc/xilinx_intc: Handle level interrupt retriggering

Acking a level sensitive interrupt should have no effect if the
interrupt pin is still asserted. The current implementation requires
and edge condition to occur for setting a level sensitive IRQ, which
means an ACK can clear a level sensitive interrupt, until the original
source strobes the interrupt again.

Fix by keeping track of the interrupt pin state and setting ISR based
on this every time update_irq() is called.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>