Update GPU inventory as a FRU property

Added:
    - YAML for FRU field.
    - Updated inventory.py data file.
    - Updated new field in the test documentation.

Resolves  openbmc/openbmc-test-automation#1307

Change-Id: I55d308cf9269e5f8ff14b577b6a058a813d43831
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/bin/generate_inventory b/bin/generate_inventory
index f17025b..ab48882 100755
--- a/bin/generate_inventory
+++ b/bin/generate_inventory
@@ -47,6 +47,7 @@
                  'State/Decorator/OperationalStatus.interface.yaml', ]
 # yaml file paths for GPU.
 yaml_gpu_list = ['Inventory/Item.interface.yaml',
+                 'Inventory/Decorator/Replaceable.interface.yaml',
                  'State/Decorator/OperationalStatus.interface.yaml', ]
 # Append to master list
 yaml_master_list.append(yaml_fru_list)