scripts: gen_handles: update to handle <zephyr/...> include prefix

Update the script so that it handles generates files using the
<zephyr/...> include prefix.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/scripts/gen_handles.py b/scripts/gen_handles.py
index a55436f..9460525 100755
--- a/scripts/gen_handles.py
+++ b/scripts/gen_handles.py
@@ -362,8 +362,8 @@
         debug("\nFinal sups:\n\t%s" % ("\n\t".join([_sn.path for _sn in n.__supports])))
 
     with open(args.output_source, "w") as fp:
-        fp.write('#include <device.h>\n')
-        fp.write('#include <toolchain.h>\n')
+        fp.write('#include <zephyr/device.h>\n')
+        fp.write('#include <zephyr/toolchain.h>\n')
 
         for dev in devices:
             hs = dev.handle