raven: some minor IRQ-related tidy-ups

raven: some minor IRQ-related tidy-ups

This really lays the groundwork for the upcoming patches: it renames the
irqs PREPPCIState struct member to pci_irqs (as soon there will be a
distinction) and then changes the raven IRQ opaque to use PREPPCIState
instead of just irqs array.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Hervé Poussineau <hpoussin@reactos.org>
Tested-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>