[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/ug/getting_started_design.md b/doc/ug/getting_started_design.md
index b8e8c46..e13bf5e 100644
--- a/doc/ug/getting_started_design.md
+++ b/doc/ug/getting_started_design.md
@@ -13,7 +13,7 @@
 
 ## Stages of a Design
 
-The life stages of a design within the OpenTitan are described in the [Hardware Development Stages]({{< relref "doc/project/hw_stages.md" >}}) document.
+The life stages of a design within the OpenTitan are described in the [Hardware Development Stages]({{< relref "doc/project/development_stages.md" >}}) document.
 This separates the life of the design into three broad stages: Specification, In Development, and Signed off.
 This document attempts to give guidance on how to get going with the first stage and have a smooth transition into the Development stage.
 They are not hard and fast rules but methods we have seen work well in the project.
@@ -76,7 +76,7 @@
 
 ## Full Design
 
-As the design develops within the OpenTitan repository, it transitions into "D0", "D1", etc., [design stages]({{< relref "doc/project/hw_stages.md" >}}) and will be eventually plugged into the top level.
+As the design develops within the OpenTitan repository, it transitions into "D0", "D1", etc., [design stages]({{< relref "doc/project/development_stages.md" >}}) and will be eventually plugged into the top level.
 Following the recommended best practices for digestible pull requests suggests that continuing to stage the design from the initial skeleton into the full featured design is a good way to make steady progress without over-burdening the reviewers.
 
 ## Top Level Inclusion