sim: Use enc capability

Now that we can dynamically query whether mcuboot is built with
encryption support, remove conditional compilation in favor of a dynamic
query.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/caps.rs b/sim/src/caps.rs
index 77be9de..dec879b 100644
--- a/sim/src/caps.rs
+++ b/sim/src/caps.rs
@@ -9,6 +9,8 @@
     EcdsaP256        = (1 << 2),
     SwapUpgrade      = (1 << 3),
     OverwriteUpgrade = (1 << 4),
+    EncRsa           = (1 << 5),
+    EncKw            = (1 << 6),
 }
 
 impl Caps {