metag: tz1090: select and instantiate irq-imgpdc

Select IMGPDC_IRQ from SOC_TZ1090 to enable the PDC interrupt controller
driver once it is merged, and instantiate it from tz1090.dtsi.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>