drm/bridge: analogix_dp: simplify analogix_dp_{set/get}_lane_link_training helpers

There is no need for separate functions for each lane, as we can deduct the
register offset to read/write from the lane index.

Signed-off-by: Wyon Bi <bivvy.bi@rock-chips.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240318203925.2837689-2-l.stach@pengutronix.de