hw/pci: add pci wrappers for allocating and asserting irqs

hw/pci: add pci wrappers for allocating and asserting irqs

Interrupt pin is selected and saved into PCI_INTERRUPT_PIN
register during device initialization. Devices should not call
directly qemu_set_irq and specify the INTx pin on each call.

Added pci_* wrappers to replace qemu_set_irq, qemu_irq_raise,
qemu_irq_lower and qemu_irq_pulse, setting the irq
based on PCI_INTERRUPT_PIN.

Added pci_allocate_irq wrapper to be used by devices that
still need PCIDevice infrastructure to assert irqs.

Renamed a static method which was named already pci_set_irq.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>