bootprogress: add OEM value for ProgressStages enumerations

This commit adds the OEM enumerations for the ProgressStages to
indicate the last stage is OEM as defined in the DSP0268_2021.2
Redfish Schema Supplement.pdf specification and DEN0069D_SBMR_2.0.pdf
document section F.2.2.

Signed-off-by: Hieu Huynh <hieuh@os.amperecomputing.com>
Change-Id: I5a2b5943df54d5208fb847c7b9e89c09af3b73cd
diff --git a/yaml/xyz/openbmc_project/State/Boot/Progress.interface.yaml b/yaml/xyz/openbmc_project/State/Boot/Progress.interface.yaml
index f079640..b064f12 100644
--- a/yaml/xyz/openbmc_project/State/Boot/Progress.interface.yaml
+++ b/yaml/xyz/openbmc_project/State/Boot/Progress.interface.yaml
@@ -56,3 +56,6 @@
           - name: MotherboardInit
             description: >
                 Motherboard/Basebord Initialization.
+          - name: OEM
+            description: >
+                OEM-defined boot progress state.