zephyr: Bring in the Zephyr build

Add support for building mcuboot as a Zephyr application.  This is
copied from the iotboot repo with some minor reorganization to work with
the mcuboot directory layout.
diff --git a/zephyr/include/syscfg/syscfg.h b/zephyr/include/syscfg/syscfg.h
new file mode 100644
index 0000000..ad58eed
--- /dev/null
+++ b/zephyr/include/syscfg/syscfg.h
@@ -0,0 +1,6 @@
+#ifndef __SYSCFG_H__
+#define __SYSCFG_H__
+
+#define MYNEWT_VAL(x) (x)
+
+#endif /* __SYSCFG_H__ */