Move rpc-if reg definitions to a header file for the preparation of adding
support for RZ/G3E XSPI that has different register definitions.
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20250424090000.136804-3-biju.das.jz@bp.renesas.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
