drm/bridge: analogix_dp: Remove duplicated code

Remove code for reading the EDID and DPCD fields and use the helpers
instead.

Besides the obvious code reduction, other helpers are being added to the
core that could be used in this driver and will be good to be able to
use them instead of duplicating them.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Cc: Javier Martinez Canillas <javier@osg.samsung.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Yakir Yang <ykk@rock-chips.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Archit Taneja <architt@codeaurora.org>