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/data/inventory.py b/data/inventory.py
index a3def69..d993a60 100644
--- a/data/inventory.py
+++ b/data/inventory.py
@@ -26,6 +26,7 @@
     "gpu": [
         "PrettyName",
         "Present",
+        "FieldReplaceable",
         "Functional"
     ]
 }