MAINTAINERS: add block driver sub-maintainers

MAINTAINERS: add block driver sub-maintainers

There are a number of contributors who maintain block drivers (image
formats and protocols).  They should be listed in the MAINTAINERS file
so that get_maintainer.pl lists them.

Note that commits are still merged through Kevin or Stefan's block tree
but the block driver sub-maintainers are usually the ones to review
patches.

Acked-by: Kevin Wolf <[email protected]>
Acked-by: Richard W.M. Jones <[email protected]>
Acked-by: Stefan Weil <[email protected]>
Acked-by: MORITA Kazutaka <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Acked-by: Jeff Cody <[email protected]>
Acked-by: Anthony Liguori <[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>