MCS: move Mode enum outside of class definition

Move Mode (EDGE/GPRS) definition and related functions outside of
GprsCodingScheme class. This allows us to use standard libosmocore
value_string functions.

Change-Id: I3baaac7f1ca3f5b88917a23c1679d63847455f47
diff --git a/src/coding_scheme.c b/src/coding_scheme.c
index 93278e7..135ddd2 100644
--- a/src/coding_scheme.c
+++ b/src/coding_scheme.c
@@ -85,3 +85,14 @@
 	OSMO_ASSERT(ht < NUM_HEADER_TYPES);
 	return hdr_type_info[ht].data_block_header_bits;
 }
+
+const struct value_string mode_names[] = {
+	{ GPRS, "GPRS" },
+	{ EGPRS_GMSK, "EGPRS_GMSK-only"},
+	{ EGPRS, "EGPRS"},
+	{ 0, NULL }
+};
+
+const char *mode_name(enum mcs_kind val) {
+	return get_value_string(mode_names, val);
+}