cmake: Fix bug where DTS_BINDINGS_DIRS could only have one entry

Fix a bug where DTS_BINDINGS_DIRS could only have one entry. When
there were more than one entry the command for invoking menuconfig
became corrupted.

This changes the separator of DTS_BINDINGS_DIR from a space to ? so
that the shell does not interpret the space as an argument separator.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
diff --git a/scripts/kconfig/kconfigfunctions.py b/scripts/kconfig/kconfigfunctions.py
index 7a5cd63..14345b6 100644
--- a/scripts/kconfig/kconfigfunctions.py
+++ b/scripts/kconfig/kconfigfunctions.py
@@ -24,7 +24,7 @@
 
     # if a board port doesn't use DTS than these might not be set
     if os.path.isfile(DTS_POST_CPP) and BINDINGS_DIRS is not None:
-        edt = edtlib.EDT(DTS_POST_CPP, BINDINGS_DIRS.split(";"))
+        edt = edtlib.EDT(DTS_POST_CPP, BINDINGS_DIRS.split("?"))
     else:
         edt = None