block: Support atomic writes limits for stacked devices

Allow stacked devices to support atomic writes by aggregating the minimum
capability of all bottom devices.

Flag BLK_FEAT_ATOMIC_WRITES_STACKED is set for stacked devices which
have been enabled to support atomic writes.

Some things to note on the implementation:
- For simplicity, all bottom devices must have same atomic write boundary
  value (if any)
- The atomic write boundary must be a power-of-2 already, but this
  restriction could be relaxed. Furthermore, it is now required that the
  chunk sectors for a top device must be aligned with this boundary.
- If a bottom device atomic write unit min/max are not aligned with the
  top device chunk sectors, the top device atomic write unit min/max are
  reduced to a value which works for the chunk sectors.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20241118105018.1870052-3-john.g.garry@oracle.com


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