drm: adv7511: Add reg_cec_offset variable to struct adv7511_chip_info

The ADV7533 and ADV7535 have an offset(0x70) for the CEC register map
compared to ADV7511. Add the reg_cec_offset variable to struct
adv7511_chip_info to handle this difference and drop the reg_cec_offset
variable from struct adv7511.

This will avoid assigning reg_cec_offset based on chip type and also
testing for multiple chip types by calling adv7533_patch_cec_registers().

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230830142358.275459-6-biju.das.jz@bp.renesas.com