libfs: Merge encrypted_ci_dentry_ops and ci_dentry_ops

In preparation to get case-insensitive dentry operations from sb->s_d_op
again, use the same structure with and without fscrypt.

Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20240221171412.10710-6-krisman@suse.de


Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>