device-tree-gpio-naming: Add power control pins

Add pins used in chassis power-on and power-off control.

Signed-off-by: Jim Wright <jlwright@us.ibm.com>
Change-Id: If5bdd4b2757a7d2e7d9c6f3d6749ddd17c51849d
diff --git a/designs/device-tree-gpio-naming.md b/designs/device-tree-gpio-naming.md
index 98ddb03..3a88e91 100644
--- a/designs/device-tree-gpio-naming.md
+++ b/designs/device-tree-gpio-naming.md
@@ -65,7 +65,13 @@
 Pattern: `power-*`
 
 Defined:
-- power-button
+#### power-button
+
+#### power-chassis-control
+Set to initiate power-on or power-off of the chassis.
+
+#### power-chassis-good
+Indicates the power good state of the chassis.
 
 ### Buttons
 Pattern: `*-button`