pcu: Add pcu_utils.h to Makefile.am

Addresses:
src/gprs_rlcmac_sched.cpp:26:23: error: pcu_utils.h: No such file or directory

Sponsored-by: On-Waves ehf
diff --git a/src/Makefile.am b/src/Makefile.am
index d1ed701..210774c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -92,7 +92,8 @@
 	sba.h \
 	rlc.h \
 	decoding.h \
-	llc.h
+	llc.h \
+	pcu_utils.h
 
 osmo_pcu_SOURCES = pcu_main.cpp