Add naive default impl for GuestMemory::find_region()

This function can be default-implemented in terms of
`GuestMemory::iter()`. Downstream impls can overwrite this more
specialized and efficient versions of course (such as GuestMemoryMmap
using a binary search).

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/guest_memory.rs

@@ -408,7 +408,9 @@ pub trait GuestMemory {
     fn num_regions(&self) -> usize;
 
     /// Returns the region containing the specified address or `None`.
-    fn find_region(&self, addr: GuestAddress) -> Option<&Self::R>;
+    fn find_region(&self, addr: GuestAddress) -> Option<&Self::R> {
+        self.iter().find(|region| addr >= region.start_addr() && addr <= region.last_addr())
+    }
 
     /// Gets an iterator over the entries in the collection.
     ///