blk: Add bounce buffer support to read/write operations

blk: Add bounce buffer support to read/write operations

Some devices have limited DMA capabilities and require that the
buffers passed to them fit specific properties. Add new optional
callback which can be used at driver level to indicate whether a
buffer alignment is suitable for the device DMA or not, and
trigger use of generic bounce buffer implementation to help use
of unsuitable buffers at the expense of performance degradation.

Signed-off-by: Marek Vasut <[email protected]>