drm/msm/dp: switch to devm_drm_bridge_add()

Make MSM DP driver use devm_drm_bridge_add() instead of plain
drm_bridge_add(). As the driver doesn't require any additional cleanup,
stop adding created bridge to the priv->bridges array.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/561639/


Signed-off-by: Rob Clark <robdclark@chromium.org>