dma40: fix DMA_SG capability and channels

The DMA_SG cap is enabled on the wrong channel, and the pointers are repeatedly
set incorrectly.  Fix it and combine the ops settings to a common function.

Acked-by: Per Forlin <per.forlin@stericsson.com>
Acked-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>