dt-bindings: display: bridge: it66121: Add compatible string for IT66122

dt-bindings: display: bridge: it66121: Add compatible string for IT66122

Add a new ite,it66122 compatible string to the IT66121 binding
documentation, since the two chips are practically same except for id
register difference.

Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Andrew Davis <afd@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20251029150636.3118628-2-nm@ti.com