prep: Use i82378 PCI->ISA bridge for 'prep' machine

prep: Use i82378 PCI->ISA bridge for 'prep' machine

Speaker I/O, ISA bus, i8259 PIC, RTC and DMA are no longer set up
individually by the machine. Effectively, no-op speaker I/O is replaced
by pcspk; PIT and i82374 DMA are introduced.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Remove related dead, alternative code.
Wire up PCI host bridge IRQs via GPIO-in IRQs of PCI->ISA bridge.

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