nds32: remove .soft_reset_halt dependency

.soft_reset_halt is not necessary for nds32 target.
Remove the dependency.

Change-Id: Ic3b126d6c7eb995583a661b762627e736222fcaa
Signed-off-by: Hsiangkai Wang <hsiangkai@gmail.com>
Reviewed-on: http://openocd.zylin.com/1612


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>