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

[ Upstream commit d89078c3

 ]

In order to avoid any probe ordering issue, the best practice is to move
the secondary MIPI-DSI device registration and attachment to the
MIPI-DSI host at probe time. Let's do this.

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20211025151536.1048186-7-maxime@cerno.tech
Stable-dep-of: 941882a0

 ("drm/bridge: lt8912b: Fix bridge_detach")
Signed-off-by: Sasha Levin <sashal@kernel.org>