drm: renesas: rz-du: Drop DU_MCR0_DPI_OE macro

The DPI_OE bit is removed from the latest RZ/G2UL and RZ/G2L hardware
manual. So, drop this macro.

Fixes: b330f148 ("drm: renesas: rz-du: Add RZ/G2UL DU Support")
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241022082433.32513-2-biju.das.jz@bp.renesas.com