drm/bridge: anx7625: Add bridge helper atomic conversion

Add bridge helper atomic conversion.

Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220106100127.1862702-1-xji@analogixsemi.com