ld: pru: Add pru_irq_map output section * scripttempl/pru.sc (.pru_irq_map): Define output section. * testsuite/ld-pru/pru_irq_map-1.d: New test. * testsuite/ld-pru/pru_irq_map-2.d: New test. * testsuite/ld-pru/pru_irq_map.s: New test.