Add mkbootfs to build-tools am: 05274b3a78

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/1688282

Change-Id: I287f032ea6cafd8a65a8c18e0de52148a2f77a86
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index 9b9d261..53463c2 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -71,6 +71,7 @@
         hidl-lint
         m4
         make
+        mkbootfs
         ninja
         one-true-awk
         openssl