irqchip/msi-lib: Add IRQ_DOMAIN_FLAG_FWNODE_PARENT handling

In some irqchip implementations the fwnode representing the IRQdomain
and the MSI controller fwnode do not match; in particular the IRQdomain
fwnode is the MSI controller fwnode parent.

To support selecting such IRQ domains, add a flag in core IRQ domain
code that explicitly tells the MSI lib to use the parent fwnode while
carrying out IRQ domain selection.

Update the msi-lib select callback with the resulting logic.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250703-gicv5-host-v7-27-12e71f1b3528@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>