board: renesas: remove empty board_early_init_f function

Remove empty board_early_init_f function, since it is disabled
in ebisu and condor board configs.

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