can: rcar_canfd: Add sh variable to struct rcar_canfd_hw_info

can: rcar_canfd: Add sh variable to struct rcar_canfd_hw_info

R-Car Gen3 and Gen4 have some differences in the shift bits. Introduce a
struct rcar_canfd_shift_data to hold these values and add the struct
rcar_canfd_shift_data variable sh to struct rcar_canfd_hw_info to handle
these differences. After this, drop the unused functions reg_gen4() and
is_gen4().

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://patch.msgid.link/20250417054320.14100-17-biju.das.jz@bp.renesas.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>