mvebu arm for 5.3 (part 1)

Document the git repository for the mvebu entry of the MAINTAINER file

* tag 'mvebu-arm-5.3-1' of git://git.infradead.org/linux-mvebu:
  MAINTAINERS: mvebu: Add git entry
Signed-off-by: Olof Johansson <olof@lixom.net>