Mark libs as double_loadable

libs (libmedia_helper, libstagefright_omx_utils, libstagefright_xmlparser)
are VNDK and also used by LLNDK(libmediandk) which means these libs can be double-loaded.
(deps:
 - libmediandk -> libmedia -> libaudioclient -> libmedia_helper
 - libmediandk -> libmedia_jni -> libstagefright -> libstagefright_omx_utils
 - libmediandk -> libmedia_jni -> libstagefright -> libstagefright_xmlparser
)

Bug: 121280180
Test: m -j
Change-Id: Ibbf5dede1f503e86484f805b252d4ced779445cb