zephyr: Add VERSION file

Adds a file which contains the current MCUboot code version, which
can be used by Zephyr builds.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/boot/zephyr/VERSION b/boot/zephyr/VERSION
new file mode 100644
index 0000000..465a403
--- /dev/null
+++ b/boot/zephyr/VERSION
@@ -0,0 +1,5 @@
+VERSION_MAJOR = 1
+VERSION_MINOR = 11
+PATCHLEVEL = 99
+VERSION_TWEAK = 0
+EXTRAVERSION = dev