bus: mvebu-mbus: Remove open coded "ranges" parsing

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

Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20230216181204.2895676-1-robh@kernel.org


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