piix4: Add an i8259 Interrupt Controller as specified in datasheet

piix4: Add an i8259 Interrupt Controller as specified in datasheet

Add ISA irqs as piix4 gpio in, and CPU interrupt request as piix4 gpio out.
Remove i8259 instanciated in malta board, to not have it twice.

We can also remove the now unused piix4_init() function.

Acked-by: Michael S. Tsirkin <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Signed-off-by: Hervé Poussineau <[email protected]>
Message-Id: <20171216090228[email protected]>
Reviewed-by: Aleksandar Markovic <[email protected]>
[PMD: rebased, updated includes, use ISA_NUM_IRQS in for loop]
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>