docs: kdoc: split the processing of the two remaining inline states

docs: kdoc: split the processing of the two remaining inline states

Now that "inline_*" are just ordinary parser states, split them into two
separate functions, getting rid of some nested conditional logic.

The original process_inline() would simply ignore lines that didn't match
any of the regexes (those lacking the initial " * " marker).  I have
preserved that behavior, but we should perhaps emit a warning instead.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>