params: Introduce the param_unknown_fn type

Introduce a new type for the callback to parse an unknown argument.
This unifies function prototypes which takes that as a parameter.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231120151419.1661807-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Kees Cook <keescook@chromium.org>