libublksrv: move common utilities helpers into public header

Add utils.h for holding this common util helpers.

Signed-off-by: Ming Lei <[email protected]>
diff --git a/include/ublksrv_tgt.h b/include/ublksrv_tgt.h
index 5145ea4..0ac70e3 100644
--- a/include/ublksrv_tgt.h
+++ b/include/ublksrv_tgt.h
@@ -8,8 +8,7 @@
 #include <iostream>
 #include <type_traits>
 
-//we are free to use the private definition
-#include "ublksrv_priv.h"
+#include "ublksrv.h"
 
 #define ublk_assert(x)  do { \
 	if (!(x)) {	\