Refactor DTS files for Zynq-based SoCs

• Factor out common part to zynq-7000.dtsi
• Fix problem with Zynq interrupts by using interrupt "triples" in .dtsi file to differentiate between edge-triggered and level-triggered interrupts
• cgem driver now recognizes "status" property

Submitted by: Thomas Skibo <thomasskibo@yahoo.com>
Differential Revision: https://reviews.freebsd.org/D6095