List drm HALs from manifest

To support lazy drm HALs, libmediadrm needs to list all available HALs
that are defined in the manifest. Otherwise, it will only list HALs that
are currently running. This change is necessary because lazy HALs do not
run until they are requested. Without this change, libmediadrm would not
be aware that the lazy HALs are present, and it would not know to call
getService() to start them.

Test: Run gts
Bug: 112386116
Change-Id: I9b41c60d574b9c8c857b8838a5bbdc64388c9ddb