Merge patch series "fs: btrfs: add support for readdir"

Alexey Charkov <alchark@flipper.net> says:

Btrfs in U-boot currently uses a custom callback for ls and doesn't
expose the standard opendir/readdir/closedir interface, making it harder
to use in generic code. One area where this would be useful is in
discovering BLS type 1 entries [1] on a Btrfs filesystem.

Add support for the standard interface, and implement ls in terms of it.

[1] https://lore.kernel.org/u-boot/20260604-bls-v1-0-4ce6d1ee4711@flipper.net/
Link: https://lore.kernel.org/r/20260626-btrfs-readdir-v2-0-7dd43f72d1b4@flipper.net