move get_string_value() und get_value_string() into debug.c

this makes bsc_mgcp and ipaccess-proxy compile again
diff --git a/openbsc/src/debug.c b/openbsc/src/debug.c
index acfcba3..90a9fc7 100644
--- a/openbsc/src/debug.c
+++ b/openbsc/src/debug.c
@@ -56,6 +56,32 @@
     [DREF]	= { .enabled = 0, .loglevel = LOGL_NOTICE },
 };
 
+const char *get_value_string(const struct value_string *vs, u_int32_t val)
+{
+	int i;
+
+	for (i = 0;; i++) {
+		if (vs[i].value == 0 && vs[i].str == NULL)
+			break;
+		if (vs[i].value == val)
+			return vs[i].str;
+	}
+	return "unknown";
+}
+
+int get_string_value(const struct value_string *vs, const char *str)
+{
+	int i;
+
+	for (i = 0;; i++) {
+		if (vs[i].value == 0 && vs[i].str == NULL)
+			break;
+		if (!strcasecmp(vs[i].str, str))
+			return vs[i].value;
+	}
+	return -EINVAL;
+}
+
 struct debug_info {
 	const char *name;
 	const char *color;