drm: bridge: adv7511: enable CEC support for ADV7535

Like the ADV7533, the ADV7535 has an offset for the CEC register map,
and it is the same value (ADV7533_REG_CEC_OFFSET = 0x70).

Rather than testing for numerous chip types in the offset calculations
throughout the driver, just compute it during driver probe and put it in
the private adv7511 data structure.

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220423120854.1503163-2-alvin@pqrs.dk