kernel-doc: check for extra kernel-doc notations

Add functionality to check for function parameters or structure (or
union/typedef/enum) field members that are described in kernel-doc but
are not part of the expected (declared) parameters or structure.
These generate warnings that are called "Excess" descriptions.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>