sim: Test DIRECT_XIP configuration

Perform simplistic test of the DIRECT_XIP configuration (both with
single and multi-images).  This verifies that the bootloader indicates
the upgrade image should be booted.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/tests/core.rs b/sim/tests/core.rs
index 4e2d9c1..104fe79 100644
--- a/sim/tests/core.rs
+++ b/sim/tests/core.rs
@@ -59,6 +59,8 @@
 sim_test!(status_write_fails_with_reset, make_image(&NO_DEPS, true), run_with_status_fails_with_reset());
 sim_test!(downgrade_prevention, make_image(&REV_DEPS, true), run_nodowngrade());
 
+sim_test!(direct_xip_first, make_no_upgrade_image(&NO_DEPS), run_direct_xip());
+
 // Test various combinations of incorrect dependencies.
 test_shell!(dependency_combos, r, {
     // Only test setups with two images.