Rename: kvm_piix3_gsi_handlei() -> kvm_pc_gsi_handler()
        kvm_piix3_setup_irq_routing() -> kvm_pc_setup_irq_routing()

This is in preparation for other users, namely q35 at this time.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>