irq.h: fix compilation error due to missing bool type

Commit f6108d72 ("Add GICv2m support") introduced a bool return
type, but missed to include the respective header (this was probably
part of a former prerequisite series).
Fix this by including the header.

Fixes: f6108d72

 ("Add GICv2m support")
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

include/kvm/irq.h

 #ifndef KVM__IRQ_H
 #define KVM__IRQ_H
 
+#include <stdbool.h>
 #include <linux/types.h>
 #include <linux/rbtree.h>
 #include <linux/list.h>