powerpc/4xx: Complete removal of MSI support

Finish the work by removing all references to the PPC4xx_MSI config
and the associated device nodes in the DTs.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/e92f2bb3-b5e1-c870-8151-3917a789a640@kaod.org