zephyr: migrate includes to <zephyr/...>

Zephyr has prefixed all of its includes with <zephyr/...>. While the
_old_ mode can still be used (CONFIG_LEGACY_INCLUDE_PATH) and is still
enabled by default, it's better to be prepared for its removal in the
future.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
diff --git a/boot/zephyr/include/target.h b/boot/zephyr/include/target.h
index 97365c2..5562434 100644
--- a/boot/zephyr/include/target.h
+++ b/boot/zephyr/include/target.h
@@ -19,9 +19,9 @@
  * Otherwise, the Zephyr SoC header and the DTS provide most
  * everything we need.
  */
-#include <devicetree.h>
+#include <zephyr/devicetree.h>
 #include <soc.h>
-#include <storage/flash_map.h>
+#include <zephyr/storage/flash_map.h>
 
 #define FLASH_ALIGN FLASH_WRITE_BLOCK_SIZE