core cpu: add defaulttransceiver pseudomodule

update examples/default
make: add Makefile.pseudomodules and use it

BASELIBS now defines targets for anything in USEMODULE that is not in PSEUDOMODULES
move defaulttransceiver to Makefile.pseudomodules
tests/test_net_if: use defaulttransceiver
tests/test_net_if: update BLACKLIST/WHITELIST
tests/test_pnet: use defaulttransceiver