boot_serial: Add image state set/get

Adds optional image state set/get functionality to serial recovery
mode which allows for listing image states and marking images to
be tested or as confirmed.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig.serial_recovery b/boot/zephyr/Kconfig.serial_recovery
index c73573b..4d8f92f 100644
--- a/boot/zephyr/Kconfig.serial_recovery
+++ b/boot/zephyr/Kconfig.serial_recovery
@@ -207,4 +207,12 @@
 	  If y, image list responses will include the image hash (adds ~100
 	  bytes of flash).
 
+config BOOT_SERIAL_IMG_GRP_IMAGE_STATE
+	bool "Image state support"
+	depends on !SINGLE_APPLICATION_SLOT
+	select BOOT_SERIAL_IMG_GRP_HASH if UPDATEABLE_IMAGE_NUMBER > 1
+	help
+	  If y, image states will be included with image lists and the set
+	  state command can be used to mark an image as test/confirmed.
+
 endif # MCUBOOT_SERIAL