drivers/interrupt_controller: shared_irq: configure by device tree

This allows the shared_irq driver to be configured by device tree.
With previous implementation, only the board configuration can
override the IRQ trigger, as the trigger config is a "choice" rather
than "config". With this patch, the driver can be fully configued at
the SoC level.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>