make: easify {sys,drivers}/Makefile

Currently you need to add every new sys and driver module into the
respective Makefile. This requires rebasing if another module was merged
in the meantime.

This PR allows you to omit the entry to {sys,drivers}/Makefile, if the
subfolder has the same name as the module name, which should be sensible
in most cases.
exchanged BOARD_BLACKLIST with FEATURES_REQUIRED in the example Makefile
added cpp as feature for board native
Merge pull request #1988 from BytesGalore/riot_and_cpp_blacklist_to_required_feature

examples/riot_and_cpp: exchanged BOARD_BLACKLIST with FEATURES_REQUIRED
board/udoo: added RNG configuration
Merge pull request #1986 from Kijewski/smaller-sys_makefile

make: easify {sys,drivers}/Makefile
Merge pull request #1992 from haukepetersen/add_udoo_random

board/udoo: added RNG configuration
Add UBJSON library