memory: add memory_region_is_rom()

Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/memory.c b/memory.c
index 4264b42..01baeac 100644
--- a/memory.c
+++ b/memory.c
@@ -1074,6 +1074,11 @@
     return mr->ram;
 }
 
+bool memory_region_is_rom(MemoryRegion *mr)
+{
+    return mr->ram && mr->readonly;
+}
+
 void memory_region_set_offset(MemoryRegion *mr, target_phys_addr_t offset)
 {
     mr->offset = offset;