dm: core: downgrade some dm_warn messages to log_debug()

dm: core: downgrade some dm_warn messages to log_debug()

People complained that enabling (SPL_)DM_WARN was now totally unusable
due to the amount of messages printed on the console.

Let's downgrade the log level of some messages that are clearly not on
the error path.

Note that there's one pr_debug in there, because it is followed by
pr_cont so it made sense to reuse the same family of functions.

Reported-by: Alexander Dahl <ada@thorsis.com>
Fixes: 6afdb1585112 ("dm: core: migrate debug() messages to use dm_warn")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Simon Glass <sjg@chromium.org>