MAINTAINERS: add all-match entry for qemu-devel@

Add an entry to MAINTAINERS that matches every patch, and requests the
user send patches to qemu-devel@nongnu.org.

It's not 100% obvious to project newcomers that all patches should be sent
there; checkpatch doesn't say so, and since it mentions other lists to CC,
the wording "the list" from the SubmitAPatch wiki page can be taken
to mean only those lists, not the main list too.

The F: entries were taken from a similar entry in the Linux kernel.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Message-Id: <1454987065-12961-1-git-send-email-swarren@wwwdotorg.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
