dt-bindings: bus: renesas-bsc: allow additional properties

Allow additional properties to enable devices attached to the bus.
Fixes warnings like these:

arch/arm/boot/dts/renesas/sh73a0-kzm9g.dtb: bus@fec10000 (renesas,bsc-sh73a0): Unevaluated properties are not allowed ('ethernet@10000000' was unexpected)
arch/arm/boot/dts/renesas/r8a73a4-ape6evm.dtb: bus@fec10000 (renesas,bsc-r8a73a4): Unevaluated properties are not allowed ('ethernet@8000000', 'flash@0' were unexpected)

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>