dt-bindings: memory: renesas,rpc-if: Add optional interrupts property

For completeness add optional interrupts property.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211025205631.21151-3-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>