board: silinux: Enable recovery SPL for EK874 board

Enable building SPL for EK874 board which is based on R8A774C0 SoC.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>