Add check to update-makefiles.sh.

Now that we also have packages like android.hidl.base which reside in
system/libhidl/transport which are read in by hidl-gen (see
-randroid.hidl:system/libhidl/transport in the same file), we can
display a pretty warning message if they are missing.

We'll have to remember to update this after b/33276472.

Test: ran update-makefiles.sh
Change-Id: Ia3e3183dd5139cf3a8d1bf7bd25c201d1b098c79