MAINTAINERS: Add Andreas Larsson as co-maintainer for arch/sparc

Dave has not been very active on arch/sparc for the past two years.
I have been contributing to the SPARC32 port as well as maintaining
out-of-tree SPARC32 patches for LEON3/4/5 (SPARCv8 with CAS support)
since 2012. I am willing to step up as an arch/sparc (co-)maintainer.

For recent discussions on the matter, see [1] and [2].

[1] https://lore.kernel.org/r/20230713075235.2164609-1-u.kleine-koenig@pengutronix.de
[2] https://lore.kernel.org/r/20231209105816.GA1085691@ravnborg.org/

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Acked-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>