omap_hsmmc: be more conservative with dma params

omap_hsmmc: be more conservative with dma params

dgame reported something what seems to be a SD read corruption he is
getting after a palemoon crash. After more testing done by him it
seems to be caused by 9e0b4807ca06, so only limit the tuned params
to MMC3 now to still get the wifi benefit.

Also revert parameters that are not helping wifi, just to be safe:
- OMAP_DMA_DST_SYNC_PREFETCH
- OMAP_DMA_WRITE_LAST_NON_POSTED

Testing is difficult and only dgame can reproduce it, so the exact
cause of his issue remains unclear.