prep: Use pc87312 device instead of collection of random ISA devices

prep: Use pc87312 device instead of collection of random ISA devices

We can't however replace the built-in IDE controller, as the one in
pc87312 is only single-channel and can use only IRQ 14. Therefore the
pc87312's IDE function gets disabled via the config property.

PReP emulation also gains a parallel port emulation this way.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
[AF: Use TYPE_PC87312 constant, add to ppc64-softmmu and to MAINTAINERS]
Signed-off-by: Andreas Färber <andreas.faerber@web.de>