Revert "drm/bridge: lt8912b: Register and attach our DSI device at probe"

This reverts commit ef4a4095 which is
commit d89078c3 upstream.

The commit was applied to make further commits apply cleanly, but the
commit depends on other commits in the same patchset. I.e. the
controlling DSI host would need a change too. Thus one would need to
backport the full patchset changing the DSI hosts and all downstream
DSI device drivers.

Revert the commit and fix up the conflicts with the backported fixes
to the lt8912b driver.

Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>