dtc: Make many functions 'static'

This patch marks various functions not shared between c files
'static', as they should be.  There are a couple of functions in dtc,
and many in the testsuite.

This is *almost* enough to enable the -Wmissing-prototypes warning.
It's not quite enough, because there's a mess of junk in the flex
generated code which triggers that warning which I'm not yet sure how
to deal with.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

data.c

@@ -217,7 +217,7 @@ struct data data_insert_at_marker(struct data d, struct marker *m,
 	return d;
 }
 
-struct data data_append_markers(struct data d, struct marker *m)
+static struct data data_append_markers(struct data d, struct marker *m)
 {
 	struct marker **mp = &d.markers;