Avoid inlining all and everything from alloc_cache.h and move cold bits
into a new file.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/06984c6cd58e703f7cfae5ab3067912f9f635a06.1738087204.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>