compat: add compatibility definitions for old MM_MODEM_BAND_EUTRAN_* values

Those Roman numeral suffixes in MM_MODEM_BAND_EUTRAN_* were replaced
with 1, 2, 3, ..., etc. This patch adds a compatibility header,
ModemManager-compat.h, to alias the old MM_MODEM_BAND_EUTRAN_* values to
the new values.

docs/reference/api/ModemManager-docs.xml

@@ -90,6 +90,11 @@
   <!-- Part 3, Migration reference -->
   <xi:include href="xml/ModemManager-migration-reference.xml"/>
 
+  <part id="ref-compat">
+    <title>Compatibility with older versions</title>
+    <xi:include href="xml/mm-compat.xml"/>
+  </part>
+
   <index>
     <title>Index</title>
   </index>