aha1542: use a local bounce buffer

To remove the last user of the unchecked_isa_dma flag and thus the block
layer ISA bounce buffering switch this driver to use its own local bounce
buffer.  This has the effect of not needing the chain indirection and
supporting and unlimited number of segments.  It does however limit the
transfer size for each command to something that can be reasonable
allocated by dma_alloc_coherent like 8K.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210331073001.46776-2-hch@lst.de


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