MAINTAINERS: add an entry for StarFive devicetrees

Emil looks after the downstream StarFive stuff, and agreed to look after
the upstream ones too.

CC: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Emil Renner Berthing <kernel@esmil.dk>
Link: https://lore.kernel.org/r/20221109212219.1598355-4-conor@kernel.org


Signed-off-by: Arnd Bergmann <arnd@arndb.de>