l4t-graphics-demos: disable parallel make

Builds with the recently-introduced make 4.4 are broken, with a race
between building and using the internal libraries (particularly
libnvtexfont2.a).  The makefile rules don't look completely race-proof,
which is probably the root cause, although it's possible there's a bug
in make.  For now, we'll just disable parallel builds of this recipe.

Signed-off-by: Matt Madison <matt@madison.systems>

recipes-graphics/l4t-graphics-demos/l4t-graphics-demos_35.1.0.bb

@@ -22,6 +22,8 @@ PACKAGECONFIG[wayland] = ",,libxkbcommon wayland wayland-native weston libffi vi
 
 CONFIGURESTAMPFILE = "${WORKDIR}/configure.sstate"
 
+PARALLEL_MAKE = ""
+
 do_configure() {
     if [ -n "${CONFIGURESTAMPFILE}" ]; then
         if [ -e "${CONFIGURESTAMPFILE}" ]; then