cpu: add socket default

Implementations need not provide the socket information.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: I874692061c4d61669017db27ac8fc57dfd980ea9
diff --git a/yaml/xyz/openbmc_project/Inventory/Item/Cpu.interface.yaml b/yaml/xyz/openbmc_project/Inventory/Item/Cpu.interface.yaml
index 222f117..7acf354 100644
--- a/yaml/xyz/openbmc_project/Inventory/Item/Cpu.interface.yaml
+++ b/yaml/xyz/openbmc_project/Inventory/Item/Cpu.interface.yaml
@@ -5,6 +5,7 @@
       type: string
       description: >
           Processor Socket designation on MotherBoard.
+      default: ""
     - name: Family
       type: string
       description: >