drm/bridge: prevent encoder chain changes while iterating with list_for_each_entry_from()

drm/bridge: prevent encoder chain changes while iterating with list_for_each_entry_from()

These loops in drm_bridge.c iterate over the encoder chain using
list_for_each_entry_from(), which does not prevent changes to the bridge
chain while iterating over it.

Convert most of those loops to instead use
drm_for_each_bridge_in_chain_from(), which locks the chain.

This also simplifies code.

All the "simple" loops are converted here. The only ones not touched are
those in drm_atomic_bridge_chain_pre_enable() and
drm_atomic_bridge_chain_post_disable(), because they have nested loops
which are not well handled by drm_for_each_bridge_in_chain_from(). Those
two functions are handled by a separate commit.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://patch.msgid.link/20260324-drm-bridge-alloc-encoder-chain-mutex-v5-5-8bf786c5c7e6@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>