staging: unisys: update MAINTAINERS and TODO

This patch adds the Unisys s-Par driver maintainers to the MAINTAINERS
file, changes the state to "Supported", modifies TODO to address patches
to the Unisys mailing list, and adds Greg Kroah-Hartman to the patch
recipients list.

Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>