zephyr: migrate upgrade-only to Kconfig
Handle CONFIG_BOOT_UPGRADE_ONLY in mcuboot_config.h, and switch the
release test Makefile to using an OVERLAY_CONFIG fragment.
This removes the last user of the Makefile BOOTLOADER_CONFIG variable,
so delete it as well.
Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>
diff --git a/samples/zephyr/overlay-upgrade-only.conf b/samples/zephyr/overlay-upgrade-only.conf
new file mode 100644
index 0000000..bdff7ac
--- /dev/null
+++ b/samples/zephyr/overlay-upgrade-only.conf
@@ -0,0 +1,2 @@
+# Kconfig overlay for building in upgrade-only mode.
+CONFIG_BOOT_UPGRADE_ONLY=y