west: Add a boards command

Add a new "boards" command that is able to list all the boards in the
upstream tree. There is currently no support for out-of-tree boards.

The command executes cmake to use the built-in CMake script,
boards.cmake, to list the boards, and then stores the information
retrieved and allows the user to present it in a user-definable format.

Fixes https://github.com/zephyrproject-rtos/west/issues/53

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
6 files changed