dma-mapping: mn10300: remove the obsolete and unnecessary DMA API comments
pci_dma_sync_single was obsoleted long ago.
All the comments are generic, not architecture specific, simply describes
some of the DMA-API (and the same comments are in other files).
Documentation/DMA-API.txt have more detailed descriptions.
This removes the above obsolete and unnecessary DMA API
comments. Let's describe the DMA API in only
Documentation/DMA-API.txt.