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/hal/hal_flash.h b/zephyr/include/hal/hal_flash.h
new file mode 100644
index 0000000..2895479
--- /dev/null
+++ b/zephyr/include/hal/hal_flash.h
@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#ifndef H_HAL_FLASH_
+#define H_HAL_FLASH_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <inttypes.h>
+
+int hal_flash_read(uint8_t flash_id, uint32_t address, void *dst,
+  uint32_t num_bytes);
+int hal_flash_write(uint8_t flash_id, uint32_t address, const void *src,
+  uint32_t num_bytes);
+int hal_flash_erase_sector(uint8_t flash_id, uint32_t sector_address);
+int hal_flash_erase(uint8_t flash_id, uint32_t address, uint32_t num_bytes);
+uint8_t hal_flash_align(uint8_t flash_id);
+int hal_flash_init(void);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* H_HAL_FLASH_ */