mailmap: add entries for Richard Leitner

Map all my old email addresses to my current address.

Link: https://lkml.kernel.org/r/20230316-my-mailmap-v1-1-76bc3a36ba41@linux.dev


Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>