assemble_vintf: adding avb.vbmeta-version into framework compatiblity matrix

Bug: 38325029
Test: builds system.img, checks $OUT/system/compatibility_matrix.xml
      contains correct vbmeta-version

Change-Id: Ib2eee1a98c833aebac4845ebdb531009b53dd2e2
diff --git a/assemble_vintf.cpp b/assemble_vintf.cpp
index 62d65b0..05801eb 100644
--- a/assemble_vintf.cpp
+++ b/assemble_vintf.cpp
@@ -118,6 +118,12 @@
             }
             matrix->framework.mSepolicy =
                 Sepolicy(kernelSepolicyVers, {{sepolicyVers.majorVer, sepolicyVers.minorVer}});
+
+            Version avbMetaVersion;
+            if (!getFlag("FRAMEWORK_VBMETA_VERSION", &avbMetaVersion)) {
+                return false;
+            }
+            matrix->framework.mAvbMetaVersion = avbMetaVersion;
         }
         out() << gCompatibilityMatrixConverter(*matrix);
         out().flush();