thunderbolt: ctl: Fix kernel-doc descriptions of non-static functions

Fix kernel-doc descriptions of all non-static functions and struct
tb_cfg. Gets rid of several warnings on W=1 builds too.

Reported-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Lee Jones <lee.jones@linaro.org>