Activation: Add Staging state

The process of staging a firmware image may take a period of time.
Use this as an intermediate state between Ready and Staged.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3e29bedc3bda2525b9878e9dd60d0fd8488e0d78
diff --git a/xyz/openbmc_project/Software/Activation.interface.yaml b/xyz/openbmc_project/Software/Activation.interface.yaml
index efeeeb6..6af2984 100644
--- a/xyz/openbmc_project/Software/Activation.interface.yaml
+++ b/xyz/openbmc_project/Software/Activation.interface.yaml
@@ -38,6 +38,10 @@
           description: >
             The Software.Version is currently in staged flash area.
             This is moved from staged flash area to active upon reset.
+        - name: Staging
+          description: >
+            The Software.Version is currently being staged into the
+            staging flash area.
     - name: RequestedActivations
       description: >
         The possible RequestedActivation states of a Software.Version.