config: add vsn macro

The 'vsn' macro encodes the LVM2 version major, minor
and patchlevel number in a packed form using 16 bits.

lib/config/config.h

@@ -18,6 +18,10 @@
 
 #include "lvm-types.h"
 
+/* 16 bits: 3 bits for major, 4 bits for minor, 9 bits for patchlevel */
+/* Max LVM version supported: 7.15.511. Just extend bits if ever needed. */
+#define vsn(major, minor, patchlevel) (major << 13 | minor << 9 | patchlevel)
+
 struct device;
 struct cmd_context;