test: workqueue: add code description
test: workqueue: add code description

Add testcase descriptions for test_work_item_supplied_with_func(),
test_sched_delayed_work_item(), test_workqueue_max_number(),
test_workq_start_before_submit(), test_work_submit_handler()

Signed-off-by: Ying ming <d3fca11d184a89ae0a68cb35f26e2e1e6bff4322@intel.com>

Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr