MCS: move Coding Scheme enum outside of class definition

Move generic MCS enum to C header file to simplify further modifications
to GprsCodingScheme class in follow-up patches. This also allows us
to use standard libosmocore value_sting functions in upcoming patches
for IA Rest Octet encoding/decoding.

Related: OS#3014
Change-Id: I993b49d9a82b8c7ad677d52d11003794aeabe117
diff --git a/src/coding_scheme.h b/src/coding_scheme.h
new file mode 100644
index 0000000..3705ea4
--- /dev/null
+++ b/src/coding_scheme.h
@@ -0,0 +1,29 @@
+/* coding_scheme.h
+ *
+ * Copyright (C) 2015-2019 by sysmocom s.f.m.c. GmbH
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ */
+
+#pragma once
+
+enum CodingScheme {
+	UNKNOWN,
+	/* GPRS Coding Schemes: */
+	CS1, CS2, CS3, CS4,
+	/* EDGE/EGPRS Modulation and Coding Schemes: */
+	MCS1, MCS2, MCS3, MCS4, MCS5, MCS6, MCS7, MCS8, MCS9,
+	NUM_SCHEMES
+};