TLS: DTPOFF can accept offsets, stored into addendum. Remove the need of base

gas/ChangeLog:

2016-07-05  Claudiu Zissulescu  <claziss@synopsys.com>

  * config/tc-arc.c (arc_reloc_op_tag): Allow complex ops for dtpoff.
  (tc_gen_reloc): Remove passing DTPOFF base info into reloc addendum as it is
  no longer needed.

Signed-off-by: Claudiu Zissulescu <claziss@synopsys.com>