MAINTAINERS: use my kernel.org address

There were enough problems with suse.{com,cz} MTAs recently. I am bored
by restoring lost e-mails from public archives. Let's switch (all) my
MAINTAINERS addresses to @kernel.org and forward the e-mails there as I
wish.

And add the whole history to .mailmap.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Joe Perches <joe@perches.com>

Link: https://lore.kernel.org/r/20200623080919.19976-1-jslaby@suse.cz


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