pc: make pc_init1() not refer ferr_irq directly.

pc: make pc_init1() not refer ferr_irq directly.

By introducing a registering function, make pc_init1() not refer to
ferr_irq directly in order to make ferr_irq piix independent.
Later pc_init1() will be split out into another file keeping ferr_irq
static.

Signed-off-by: Isaku Yamahata <[email protected]>
Acked-by: Gerd Hoffmann <[email protected]>
Signed-off-by: Blue Swirl <[email protected]>