.mailmap: add Oleksij Rempel

I have had various email addresses and a name change after marriage.

Link: http://lkml.kernel.org/r/20181009125207.6096-1-o.rempel@pengutronix.de
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Jiri Kosina <trivial@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>