ipack: Move IndustryPack out of hw/char/

Move the header defining an IPackBus and IPackDevice base class into
a new include/ directory and move their implementation and a
PCI-IndustryPack bridge out of hw/char/ directory into a new hw/ipack/.

Acked-by: Alberto Garcia <agarcia@igalia.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>