sh: DMA driver has to specify its alignment requirements

The SH DMA driver by default uses 32-byte transfers, in this mode buffers and
sizes have to be 32-byte aligned. Specifying this requirement also fixes Oopses
with dmatest.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>