Use STATX_DIOALIGN to get direct I/O alignment

[nirs]

When using the file backend we use a pretty horrible probing mechanism to detect direct I/O
alignment size. Since Linux 6.1 we have official way to get the right value from the
kernel that works with ext4, xfs, nvme, and dm-crypt.

See https://lists.nongnu.org/archive/html/qemu-block/2022-11/msg00050.html

Tasks:

• Try to use statx to get the alignment
• If not available fallback to probing