Prepare Intel 82378 emulation for use by PReP platforms.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>

Create ISA bus in this device (suggested by Markus).
Rebase onto Memory API, mark memory ops as Little Endian.
Add VMState. Provide access to i8259 IRQs via qdev GPIOs.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Jan Kiszka <jan.kiszka@siemens.com>