zephyr: Add firmware loader MCUboot operation style

Adds a new operation style in which the secondary slot has an
image which is used to update the primary image only.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/boot/zephyr/CMakeLists.txt b/boot/zephyr/CMakeLists.txt
index 3ce4235..1356f4e 100644
--- a/boot/zephyr/CMakeLists.txt
+++ b/boot/zephyr/CMakeLists.txt
@@ -131,6 +131,11 @@
   ${BOOT_DIR}/zephyr/single_loader.c
   )
 zephyr_library_include_directories(${BOOT_DIR}/bootutil/src)
+elseif(CONFIG_BOOT_FIRMWARE_LOADER)
+zephyr_library_sources(
+  ${BOOT_DIR}/zephyr/firmware_loader.c
+  )
+zephyr_library_include_directories(${BOOT_DIR}/bootutil/src)
 else()
 zephyr_library_sources(
   ${BOOT_DIR}/bootutil/src/loader.c