Allow --disable-verification when top-level vbmeta is in 'boot'

If top-level vbmeta struct is in 'boot' partition,
the "flags" element offset of top-level vbmeta header
from the beginning of boot partition is 123 plus
top-level vbmeta offset recorded in the boot image footer.

Bug: 139639521
Test: m fastboot
Test: fastboot --disable-verification flashall
Test: fastboot --disable-verification flash boot boot.img, checks the
      flag isn't changed if the device has vbmeta partition
Test: fastboot --disable-verification flash vbmeta vbmeta.img
Change-Id: Ibf73c9330639e971ee3873ac19f072cf7baed55b
diff --git a/fastboot/Android.bp b/fastboot/Android.bp
index 546bce2..f452a64 100644
--- a/fastboot/Android.bp
+++ b/fastboot/Android.bp
@@ -189,7 +189,11 @@
     // will violate ODR.
     shared_libs: [],
 
-    header_libs: ["bootimg_headers"],
+    header_libs: [
+        "avb_headers",
+        "bootimg_headers",
+    ],
+
     static_libs: [
         "libziparchive",
         "libsparse",