use the generic dma-noncoherent code for sh V3

[Christoph Hellwig]

Hi all,

can you review these patches to switch sh to use the generic
dma-noncoherent code?  All the requirements are in mainline already
and we've switched various architectures over to it already.

Changes since V2:
 - drop a now obsolete export

Changes since V1:
 - fixed two stupid compile errors and verified them using a local
   cross toolchain instead of the 0day buildbot