irqchip/gic-v3-its: Provide MSI parent for PCI/MSI[-X]

The its_pci_msi_prepare() function from the ITS-PCI/MSI code provides the
'global' PCI/MSI domains. Move this function to the ITS-MSI parent code and
amend the function to use the domain hardware size, which is the MSI[X]
vector count, for allocating the ITS slots for the PCI device.

Enable PCI matching in msi_parent_ops and provide the necessary update to
the ITS specific child domain initialization function so that the prepare
callback gets invoked on allocations.

The latter might be optimized to do the allocation right at the point where
the child domain is initialized, but keep it simple for now.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Shivamurthy Shastri <shivamurthy.shastri@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240623142235.024567623@linutronix.de