transition: support transitioning chassis states

The is along the same lines as the host transition state commit:
https://github.com/openbmc/phosphor-dbus-interfaces/commit/9f65dfeaa5ab22cae03db45c9916868da9864f83

IBM has found a use case for also knowing when the chassis is in a
transition from On to Off or vice versa.

Some of our larger systems take a fairly significant amount of time to
power on and off their chassis's.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: Iffec13a3278f37e8ca5ca44bbe2e34970587aa37
diff --git a/xyz/openbmc_project/State/Chassis.interface.yaml b/xyz/openbmc_project/State/Chassis.interface.yaml
index 37d67e1..cc8a130 100644
--- a/xyz/openbmc_project/State/Chassis.interface.yaml
+++ b/xyz/openbmc_project/State/Chassis.interface.yaml
@@ -47,6 +47,12 @@
         - name: 'Off'
           description: >
             Chassis power is off
+        - name: 'TransitioningToOff'
+          description: >
+            Firmware is transitioning the chassis to an Off state
         - name: 'On'
           description: >
             Chassis power is on
+        - name: 'TransitioningToOn'
+          description: >
+            Firmware is transitioning the chassis to an On state