MAINTAINERS: Add information for OpenPIC

MAINTAINERS: Add information for OpenPIC

The OpenPIC interrupt controller was once the de facto standard on ppc
machines.  In qemu it's now only used on some Macintosh and the
Freescale e500 machine.  It has no listed maintainer, and as far as I
know, no-one who's really familiar with it any more.

Since I'm moving away from the area, I no longer have capacity to do even
minimal maintenance of it under the auspices of the ppc targets in general.

Therefore, this patch lists the main part of openpic, and marks it as
"Odd Fixes" to be looked after by Mark Cave-Ayland who handles the
Macintosh targets.  The openpic_kvm variant is only used on e500, so
add it to the files for that machine type (itself already Orphaned).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>