Extend list_boards.py and update boards CMake module to handle HWMv2.
list_boards.py is extended to support board.yml file in each board
folder with various information related to the board, such as vendor,
soc, cpucluster, variants, revisions.
The HWMv2 removes the requirement for a _defconfig file.
It also unifies how board revisions, cpusets, etc is defined which again
provides an option for cleaner build system implementation for handling
of boards and their integration to the build system.
The CMake boards.cmake module is updated to take advantage of the
improved design.
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>