device-tree-gpio-naming: Add host ready pins

Add pins to detect the status of HOSTs is ready or not.
Current OpenBmc support to detect Host ready via IPMI and PLDM.
However, not all of platforms support IPMI and PLDM. Some
platforms, like Ampere Mt.Jade checks input GPIO to detect host
firmware boot status.
The name of HOST ready pin has to include the index of host and
the polarity (Active high or low).

Signed-off-by: Thang Tran <thuutran@amperecomputing.com>
Change-Id: I9ce674d7637d573ef1169740a3971acea6413e12
diff --git a/designs/device-tree-gpio-naming.md b/designs/device-tree-gpio-naming.md
index 9c09058..63b3500 100644
--- a/designs/device-tree-gpio-naming.md
+++ b/designs/device-tree-gpio-naming.md
@@ -52,6 +52,19 @@
 
 #### power-button
 
+### Host Ready
+Below are input GPIO names specific to Host ready. The name of Host ready GPIO
+depends on the index of Host and the active state is high or low.
+
+Pattern:
+- `host*-ready`: Host ready, active high
+- `host*-ready-n`: Host ready, active low
+
+Defined:
+- host0-ready
+- host1-ready-n
+- ...
+
 ### LEDs
 Pattern: `led-*`