[RFC 3/4] PCI, x86: Allocate PCI IRQ on demand and free it when not used anymore

To support IOAPIC hotplug, we need to correctly manage IOAPIC pin usage, which is to allocate IRQs on demand and free them when not used anymore. So use pcibios_alloc_irq() and pcibios_free_irq() to dynamically allocate and free PCI IRQs. Also remove obseleted code mp_should_keep_irq().

[RFC 3/4] PCI, x86: Allocate PCI IRQ on demand and free it when not used anymore

To support IOAPIC hotplug, we need to correctly manage IOAPIC pin usage, which is to allocate IRQs on demand and free them when not used anymore. So use pcibios_alloc_irq() and pcibios_free_irq() to dynamically allocate and free PCI IRQs. Also remove obseleted code mp_should_keep_irq().