dt-bindings: timer: sifive,clint: Group interrupt tuples

To improve human readability and enable automatic validation, the tuples
in "interrupts-extended" properties should be grouped using angle
brackets.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-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/62bf4ee6613550c07a99d4bd226ab0d33acae4c4.1643360652.git.geert@linux-m68k.org