Break-up libaudioclient_aidl_conversion

To reduce transitive dependencies, we break out the generic parts of
libaudioclient_aidl_conversion to libaudioclient_aidl_conversion_util,
so that libaudiofoundtaion_headers could have a reduced number of
transitive dependencies (it is used in different partitions, so these
dependencies become a problem).

Test: m checkbuild
Change-Id: I1c9f385698dbc32405cc4878cd74d13e42ebb103