docs: scripts: kernel-doc: accept bitwise negation like ~@var

In some cases we'd like to indicate the bitwise negation of a parameter,
e.g.

  ~@var

This will be helpful for describing the atomic andnot operations, where
we'd like to write comments of the form:

  Atomically updates @v to (@v & ~@i)

Which kernel-doc currently transforms to:

  Atomically updates **v** to (**v** & ~**i**)

Rather than the preferable form:

  Atomically updates **v** to (**v** & **~i**)

This is similar to what we did for '!@var' in commit:

  ee2aa759 ("scripts: kernel-doc: accept negation like !@var")

This patch follows the same pattern that commit used to permit a '!'
prefix on a param ref, allowing a '~' prefix on a param ref, cuasing
kernel-doc to generate the preferred form above.

Suggested-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230605070124.3741859-25-mark.rutland@arm.com