sim: Add multi-image config support to sim

Add support for building with multiple images to the simulator.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/mcuboot-sys/Cargo.toml b/sim/mcuboot-sys/Cargo.toml
index 37dba5e..8071ba1 100644
--- a/sim/mcuboot-sys/Cargo.toml
+++ b/sim/mcuboot-sys/Cargo.toml
@@ -33,6 +33,9 @@
 # Allow bootstrapping an empty/invalid primary slot from a valid secondary slot
 bootstrap = []
 
+# Support multiple images (currently 2 instead of 1).
+multiimage = []
+
 [build-dependencies]
 cc = "1.0.25"