tests: provide MACRO to easily wrap test function to shell command

usage is as below:

TC_CMD_DEFINE(test_func_1)
TC_CMD_DEFINE(test_func_2)

static const struct shell_cmd commands[] = {
		TC_CMD_ITEM(test_func_1),
		TC_CMD_ITEM(test_func_2),
		{ NULL, NULL }
};
SHELL_REGISTER("runtest", commands);

Change-Id: I4eab67113954f373d5a2cbfaa729be180fd31444
Signed-off-by: jing wang <jing.j.wang@intel.com>