Explicitly add ART boot images to build-art-target-golem.

Golem builds the ART module with `TARGET_BUILD_UNBUNDLED=true`. When we
move the boot image out of the ART APEX, it will no longer be built.
This change solves the problem by explicitly adding ART boot images to
build-art-target-golem.

Bug: 211973309
Test: Will see the result on Golem.
Change-Id: I86f2f0e4223192cb316f446a151dabf7790774a5
1 file changed