of: property: fw_devlink: Add a devlink for panel followers

Inform fw_devlink of the fact that a panel follower (like a
touchscreen) is effectively a consumer of the panel from the purposes
of fw_devlink.

NOTE: this patch isn't required for correctness but instead optimizes
probe order / helps avoid deferrals.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.4.Ibf8e1342b5b7906279db2365aca45e6253857bb3@changeid