fdc: Parametrize ISA base, IRQ and DMA

Keep the PC values as defaults but allow to override them for PReP.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
