[doc] Update references to util/vendor.py tool.

As part of lowrisc/opentitan#607, rename references from `vendor_hw` to
`util/vendor`. Also, rename `doc/rm/vendor_hw_tool.md` as
`doc/rm/vendor_in_tool.md`.

Signed-off-by: Miguel Osorio <miguelosorio@google.com>
diff --git a/doc/rm/_index.md b/doc/rm/_index.md
index e8dc25a..4deb30d 100644
--- a/doc/rm/_index.md
+++ b/doc/rm/_index.md
@@ -5,7 +5,7 @@
    * [Topgen Tool]({{< relref "topgen_tool" >}}): Describes `topgen.py` and its Hjson format source. Used to generate rtl and validation files for top specific modules such as PLIC, Pinmux and crossbar.
    * [Register Tool]({{< relref "register_tool" >}}): Describes `regtool.py` and its Hjson format source. Used to generate documentation, rtl, header files and validation files for IP Registers and toplevel.
    * [Crossbar Tool]({{< relref "crossbar_tool" >}}): Describes `tlgen.py` and its Hjson format source. Used to generate self-documentation, rtl files of the crossbars at the toplevel.
-   * [Vendor-In Tool]({{< relref "vendor_hw_tool" >}}): Describes `vendor_hw.py` and its Hjson control file. Used to pull a local copy of code maintained in other upstream repositories and apply local patch sets.
+   * [Vendor-In Tool]({{< relref "vendor_in_tool" >}}): Describes `util/vendor.py` and its Hjson control file. Used to pull a local copy of code maintained in other upstream repositories and apply local patch sets.
 * Coding Style Guides
   * [Verilog Coding Style](https://github.com/lowRISC/style-guides/blob/master/VerilogCodingStyle.md)
   * [Python Coding Style]({{< relref "python_coding_style.md" >}})