bus: uniphier-system-bus: Remove open coded "ranges" parsing

"ranges" is a standard property and we have common helper functions for
parsing it, so let's use them.

Tested-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/20230206194503.1162108-1-robh@kernel.org


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