boards: Use a better way to find csk.board.cmake

* Use variable ZEPHYR_CSK_MODULE_DIR to locate csk folder path.

Signed-off-by: 徐宪辉 <xhxu@listenai.com>
2 job 于chore/better_way_to_find_csk_board_cmake in 7 minute 和 8 second (queued for 1 second)
状态 作业 ID 名称 覆盖率
  Ztest
已通过 #48341
zgsz-02 generic
ztest_build_only

00:04:30

已通过 #48342
zgsz-03 with-device
ztest_device_test

00:07:07