Enable IPIs on CPU 0 on arm and arm64

Not all interrupt controllers enable IPIs by default as the Arm
GIC specs make it an implementation defined option. As at least two
hypervisors have also previously masked the IPIs on boot.

As we already enable these IPIs on the non-boot CPUs it is expected
this is a safe operation.

Differential Revision:	https://reviews.freebsd.org/D26975

sys/arm64/arm64/mp_machdep.c

@@ -364,6 +364,8 @@ intr_pic_ipi_setup(u_int ipi, const char *name, intr_ipi_handler_t *hand,
 	ii->ii_send_arg = isrc;
 	strlcpy(ii->ii_name, name, INTR_IPI_NAMELEN);
 	ii->ii_count = intr_ipi_setup_counters(name);
+
+	PIC_ENABLE_INTR(intr_irq_root_dev, isrc);
 }
 
 static void