add libandroidfw_tests back to TEST_MAPPING

libandroidfw_test is not triggered when ag/15987448 modify
libandroidfw.  After the experiments in b/180720568,
`cc_test { support_host: true}` should add back to TEST_MAPPING.

Test: atest --dry-run -p frameworks/base/libs/androidfw

Bug: 180720568
Bug: 178646865
Change-Id: I5c97c860670d57504f97ef10ad296fb57176fd5c