The number of interrupts lacks an upper bound, thus assuming one,
causing properly grouped "interrupts-extended" properties to be flagged
as an error by "make dtbs_check".

Fix this by adding the missing "maxItems", using the architectural
maximum of 4095 interrupts.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/e6a4c5b20d2acb52125d7d6e6c7e3694d7cb182c.1643360652.git.geert@linux-m68k.org