imgproc: use universal intrinsic as much as possible (#9714)

* use universal intrinsic as much as possible
  * make SSE3 part as common as possible with universal intrinsic implementation
  * put the reducing part out of the main loop

* follow the comment
  * fix the typo
  * use v_reduce_sum4

* follow the comment again
  * remove all CV_SSE3 part from smooth.cpp