pinctrl: renesas: rzg2l: Drop oen_read and oen_write callbacks

pinctrl: renesas: rzg2l: Drop oen_read and oen_write callbacks

Remove oen_read and oen_write callbacks from rzg2l_pinctrl_data as
all SoCs now use the same rzg2l_read_oen() and rzg2l_write_oen()
functions directly.

Change rzg2l_read_oen() return type to int for proper error reporting
and update callers to handle errors consistently.

This simplifies the code by removing redundant callbacks and ensures
uniform OEN handling across all supported SoCs.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250806195555.1372317-8-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>