zephyr: add option for saving enckey TLVs in swap status

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/boot/zephyr/prj.conf b/boot/zephyr/prj.conf
index 30af1e4..4a5d1ec 100644
--- a/boot/zephyr/prj.conf
+++ b/boot/zephyr/prj.conf
@@ -6,6 +6,7 @@
 CONFIG_MAIN_STACK_SIZE=10240
 CONFIG_MBEDTLS_CFG_FILE="mcuboot-mbedtls-cfg.h"
 
+CONFIG_BOOT_SWAP_SAVE_ENCTLV=n
 CONFIG_BOOT_ENCRYPT_RSA=n
 CONFIG_BOOT_ENCRYPT_EC256=n