drm/bridge: imx8*-ldb: convert to devm_drm_bridge_alloc() API

This is the new API for allocating DRM bridges.

These two drivers are tangled together by the ldb_add_bridge_helper(), so
they are converted at once.

They also have a similar design, each embedding an array of channels in
their main struct, and each channel embeds a drm_bridge. This prevents
dynamic, refcount-based deallocation of the bridges.

To make the new, dynamic bridge allocation possible:

 * change the array of channels into an array of channel pointers
 * allocate each channel using devm_drm_bridge_alloc()
 * adapt ldb_add_bridge_helper() to not set the funcs pointer
   (now done by devm_drm_bridge_alloc())
 * adapt the code wherever using the channels

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Acked-by: Liu Ying <victor.liu@nxp.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250424-drm-bridge-convert-to-alloc-api-v2-31-8f91a404d86b@bootlin.com


Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>