dma40: remove "hardware link with previous jobs" code

This link in hardware with previous jobs code is:

  - unused, no clients using or requiring this feature
  - incomplete, being implemented only for physical channels
  - broken, only working to perform one link

Remove it.  This also allows us to get rid of the channel pause in the
submit_tx() routine.

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>