arm: add an interrupt rman to nexus

Allow the nexus bus to own and manage interrupt resources. Currently,
interrupt resources on this architecture are managed completely by
ofwbus, but it is desirable that system-wide memory and interrupt
resources be managed by the top-level bus.

This is a pre-requisite to moving this resource management out of
ofwbus.

Reviewed By:	ian, Elliott Mitchell <ehem+freebsd@m5p.com>
MFC after:	1 month
Differential Revision: https://reviews.freebsd.org/D32357

sys/arm/arm/nexus.c

@@ -77,6 +77,7 @@ struct nexus_device {
 #define DEVTONX(dev)	((struct nexus_device *)device_get_ivars(dev))
 
 static struct rman mem_rman;
+static struct rman irq_rman;
 
 static	int nexus_probe(device_t);
 static	int nexus_attach(device_t);
@@ -171,6 +172,12 @@ nexus_attach(device_t dev)
 	if (rman_init(&mem_rman) ||
 	    rman_manage_region(&mem_rman, 0, BUS_SPACE_MAXADDR))
 		panic("nexus_probe mem_rman");
+	irq_rman.rm_start = 0;
+	irq_rman.rm_end = ~0;
+	irq_rman.rm_type = RMAN_ARRAY;
+	irq_rman.rm_descr = "Interrupts";
+	if (rman_init(&irq_rman) || rman_manage_region(&irq_rman, 0, ~0))
+		panic("nexus_attach irq_rman");
 
 	/*
 	 * First, deal with the children we know about already
@@ -227,6 +234,10 @@ nexus_alloc_resource(device_t bus, device_t child, int type, int *rid,
 	flags &= ~RF_ACTIVE;
 
 	switch (type) {
+	case SYS_RES_IRQ:
+		rm = &irq_rman;
+		break;
+
 	case SYS_RES_MEMORY:
 	case SYS_RES_IOPORT:
 		rm = &mem_rman;