drm: bridge: adv7511: Fix build error redefinition of 'adv7511_bridge_mode_valid'

Refer to commit 9a0cdcd6("drm/bridge: adv7533:
remove dynamic lane switching from adv7533 bridge"),
remove redundant functions.

Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>