[doc] Rename Hardware -> Development Stages

In advance of adding Device Interface Function (DIF) stage tracking to
the development stages, this change renames `doc/project/hw_stages.md`
to `doc/project/development_stages.md` and updates all the links that
reference it.

Signed-off-by: Sam Elliott <selliott@lowrisc.org>
diff --git a/doc/project/_index.md b/doc/project/_index.md
index 8985af8..008bda1 100644
--- a/doc/project/_index.md
+++ b/doc/project/_index.md
@@ -8,7 +8,7 @@
 
 ## Quality standards for open hardware IP
 
-In order to gauge the quality of the different IP that is in our repository, we define a series of [Hardware Development Stages]({{< relref "hw_stages" >}}) to track the designs.
+In order to gauge the quality of the different IP that is in our repository, we define a series of [Hardware Development Stages]({{< relref "development_stages" >}}) to track the designs.
 The current status of different IP is reflected in the [Hardware Dashboard]({{< relref "hw" >}}).
 The final state for developed IP is *Signed Off*, indicating that design and verification is complete, and the IP should be bug free.
 To make it to that stage, a [Hardware Signoff Checklist]({{< relref "checklist.md" >}}) is used to confirm completion.