[ipgen] Retain version segment in instance_vlnv()

The `instance_vlnv()` template function transforms a FuseSoC VLNV string
into one specialized for the particiular template instantiation. Before,
it removed the version component of the VLNV unconditionally. Now, it
retains the version if it was present before. The version component
stays optional.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/doc/rm/ipgen_tool.md b/doc/rm/ipgen_tool.md
index d31391f..41baf9c 100644
--- a/doc/rm/ipgen_tool.md
+++ b/doc/rm/ipgen_tool.md
@@ -75,6 +75,7 @@
 
 * `instance_vlnv(vlnv)`: Transform a FuseSoC core name, expressed as VLNV string, into an instance-specific name.
   The `vendor` is set to `lowrisc`, the `library` is set to `opentitan`, and the `name` is prefixed with the instance name.
+  The optional version segment is retained.
   Use this function on the `name` of all FuseSoC cores which contain sources generated from templates and which export symbols into the global namespace.
 
 ### Templating FuseSoC core files