of/irq: Add msi-parent check to of_msi_xlate()

In some legacy platforms the MSI controller for a PCI host bridge is
identified by an msi-parent property whose phandle points at an MSI
controller node with no #msi-cells property, that implicitly
means #msi-cells == 0.

For such platforms, mapping a device ID and retrieving the MSI controller
node becomes simply a matter of checking whether in the device hierarchy
there is an msi-parent property pointing at an MSI controller node with
such characteristics.

Add a helper function to of_msi_xlate() to check the msi-parent property in
addition to msi-map and retrieve the MSI controller node (with a 1:1 ID
deviceID-IN<->deviceID-OUT  mapping) to provide support for deviceID
mapping and MSI controller node retrieval for such platforms.

Fixes: 57d72196 ("irqchip/gic-v5: Add GICv5 ITS support")
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Cc: Sascha Bischoff <sascha.bischoff@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://patch.msgid.link/20251021124103.198419-2-lpieralisi@kernel.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>