Add Zephyr config for boostrap feature

Signed-off-by: Fabio Utzig <utzig@apache.org>

boot/zephyr/Kconfig

@@ -72,6 +72,14 @@ config BOOT_UPGRADE_ONLY
 	  swapping them.  This prevents the fallback recovery, but
 	  uses a much simpler code path.
 
+config BOOT_BOOTSTRAP
+	bool "Boostrap erased slot0 from slot1"
+	default n
+	help
+	  If y, enables bootstraping support. Bootstrapping allows an erased
+	  slot0 to be initialized from a valid image in slot1.
+	  If unsure, leave at the default value.
+
 config BOOT_ENCRYPT_RSA
 	bool "Support for encrypted upgrade images"
 	default n

boot/zephyr/include/mcuboot_config/mcuboot_config.h

@@ -48,6 +48,10 @@
 #define MCUBOOT_ENCRYPT_RSA
 #endif
 
+#ifdef CONFIG_BOOT_BOOTSTRAP
+#define MCUBOOT_BOOTSTRAP 1
+#endif
+
 /*
  * Enabling this option uses newer flash map APIs. This saves RAM and
  * avoids deprecated API usage.

boot/zephyr/prj.conf

@@ -9,6 +9,8 @@ CONFIG_MBEDTLS_CFG_FILE="mcuboot-mbedtls-cfg.h"
 
 CONFIG_BOOT_ENCRYPT_RSA=n
 
+CONFIG_BOOT_BOOTSTRAP=n
+
 ### Default to RSA
 CONFIG_BOOT_SIGNATURE_TYPE_RSA=y
 CONFIG_BOOT_SIGNATURE_TYPE_ECDSA_P256=n