[nrf fromtree] cmake: store board directories in build_info

The schema for build info already contained a `board:path` sequence tag
definition, but boards.cmake did not populate this in the generated
build_info.yml.

Fix this by correctly populating the `board:path` with list of board
directories.

Signed-off-by: Torsten Rasmussen <[email protected]>
(cherry picked from commit b78c269)

Author: tejlmand

cmake/modules/boards.cmake

@@ -357,3 +357,4 @@ build_info(board name VALUE ${BOARD})
 string(REGEX REPLACE "^/" "" qualifiers "${BOARD_QUALIFIERS}")
 build_info(board qualifiers VALUE ${qualifiers})
 build_info(board revision VALUE ${BOARD_REVISION})
+build_info(board path PATH ${BOARD_DIRECTORIES})