move gsm_04_08_gprs.h to libosmocore

This requres the corresponding commit in libosmocore.
diff --git a/openbsc/src/gprs/gprs_utils.c b/openbsc/src/gprs/gprs_utils.c
index 895a033..64bfd74 100644
--- a/openbsc/src/gprs/gprs_utils.c
+++ b/openbsc/src/gprs/gprs_utils.c
@@ -20,11 +20,11 @@
  *
  */
 #include <openbsc/gprs_utils.h>
-#include <openbsc/gsm_04_08_gprs.h>
 
 #include <osmocom/core/msgb.h>
 #include <osmocom/gprs/gprs_ns.h>
 
+#include <osmocom/gsm/protocol/gsm_04_08_gprs.h>
 #include <osmocom/gsm/protocol/gsm_04_08.h>
 #include <osmocom/gsm/gsm48.h>