sim: add Mbed TLS EC256 encrypted image support

Add new feature that allows testing EC256 encrypted images using the
Mbed TLS backend.

Move config-ecdsa.h to config-ec.h because definitions are very similar
between ECDSA and ECDH with Mbed TLS so resort to a single config file.

Add new feature and fix the build; add proper Mbed TLS memory
initialization when enc-ec256-mbedtls is used.

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/sim/mcuboot-sys/csupport/run.c b/sim/mcuboot-sys/csupport/run.c
index 0133262..2bea140 100644
--- a/sim/mcuboot-sys/csupport/run.c
+++ b/sim/mcuboot-sys/csupport/run.c
@@ -231,7 +231,8 @@
     struct boot_loader_state *state;
 
 #if defined(MCUBOOT_SIGN_RSA) || \
-    (defined(MCUBOOT_SIGN_EC256) && defined(MCUBOOT_USE_MBED_TLS))
+    (defined(MCUBOOT_SIGN_EC256) && defined(MCUBOOT_USE_MBED_TLS)) ||\
+    (defined(MCUBOOT_ENCRYPT_EC256) && defined(MCUBOOT_USE_MBED_TLS))
     mbedtls_platform_set_calloc_free(calloc, free);
 #endif