Make libavb and libavb_headers vendor_ramdisk_available.

This is needed to make libfs_mgr vendor_ramdisk_available.

Bug: 193833730
Test: builds
Change-Id: I12eb065de7913781e7cdbe06a1fa87da7119624d

Android.bp

diff --git a/Android.bp b/Android.bp
index 6e438d8..6685ab2 100644
--- a/Android.bp
+++ b/Android.bp
@@ -157,6 +157,7 @@
     ],
     host_supported: true,
     ramdisk_available: true,
+    vendor_ramdisk_available: true,
     recovery_available: true,
     header_libs: [
         "avb_headers",
@@ -378,6 +379,7 @@
     name: "avb_headers",
     host_supported: true,
     ramdisk_available: true,
+    vendor_ramdisk_available: true,
     recovery_available: true,
     export_include_dirs: ["."],
     target: {