drm/bridge: ps8640: Use atomic variants of drm_bridge_funcs

The atomic variants of enable/disable in drm_bridge_funcs are the
preferred operations - introduce these.

The ps8640 driver used the non-atomic variants of the drm_bridge_chain_pre_enable/
drm_bridge_chain_post_disable - convert these to the atomic variants.

v2:
  - Init state operations in drm_bridge_funcs (Laurent)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Cc: Jitao Shi <jitao.shi@mediatek.com>
Cc: Philip Chen <philipchen@chromium.org>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221205173328.1395350-2-dave.stevenson@raspberrypi.com
Signed-off-by: Maxime Ripard <maxime@cerno.tech>