drm/vc4: dsi: Remove splitting the bridge chain from the driver

Splitting the bridge chain fails for atomic bridges as the
framework can't add the relevant state in
drm_atomic_add_encoder_bridges.
The chain was split because we needed to power up before
calling pre_enable, but that is now done in mode_set, and will
move into the framework.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221207-rpi-dsi-bridge-v1-3-8f68ee0b0adb@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>