tcl at91samdXX.cfg: update config to current OpenOCD status

tcl at91samdXX.cfg: update config to current OpenOCD status

Remove comment about workaround of not working 'reset halt' - not needed
as 'reset halt' is working as expected @ EDBG with srst_only.
Add srst_pulls_trst to reset_config as it no more triggers an error.

Change-Id: I47cf445690c46ccfb866900cddbfcaefc8649f82
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3722
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>