onclite: Enforce vendor tree presence

A compiled build has no chance of booting without the prebuilt
binaries, so fail the build if those are not present.

Signed-off-by: Hadad <hadad@linuxmail.org>
Change-Id: I8124a5f92a75490ce48422b9d760764733efe37e
Signed-off-by: SirRGB <sirrgb@proton.me>