ibm: Error interface for blank system VPD.

This commit adds error interface to handle blank system VPD in
case of system VPD restore.
For system VPD restore, VPD data is first checked at the EEPROM
path, if blank then the data from DBus is used to re-store. In
case where VPD data is blank at both EEPROM path and Dbus cache
the process of system VPD restore fails and hence PEL is logged
in that scenario.
This interface serves as the key into the message registry, and
is the Message property of the OpenBMC event log that the PEL is
being created from.

Signed-off-by: Sunny Srivastava <sunnsr25@in.ibm.com>
Change-Id: Ieac334a1819a31e3964abde3a326106f2ab2ec62
diff --git a/com/ibm/VPD.errors.yaml b/com/ibm/VPD.errors.yaml
index 8f9cdeb..c2708ac 100644
--- a/com/ibm/VPD.errors.yaml
+++ b/com/ibm/VPD.errors.yaml
@@ -8,3 +8,8 @@
   description: Record not found.
 - name: KeywordNotFound
   description: Keyword is not found.
+- name: BlankSystemVPD
+  description: System VPD is blank on both hardware and cache.
+               On IBM systems, certain VPD data must be available
+               for the system to boot. This error is used to
+               indicate that no valid data was found by the BMC.