MAINTAINERS: add mvpp2 driver entry

Since its creation Marvell NIC driver for Armada 375/7k8k and
CN913x SoC families mvpp2 has been lacking an entry in MAINTAINERS,
which sometimes lead to unhandled bugs that persisted
across several kernel releases.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20201211165114.26290-1-mw@semihalf.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>