fix NEON port, use vget_lane_*() instead of temporary variables (saves extra load/store), following advice by  Josh Bleecher Snyder <josharian@gmail.com>. Also implement pmadd() using vmla instead of nested padd/pmul.
fix NEON port, use vget_lane_*() instead of temporary variables (saves extra
load/store), following advice by  Josh Bleecher Snyder <josharian@gmail.com>.
Also implement pmadd() using vmla instead of nested padd/pmul.

madlib/eigen_backup,madlib/eigen_backup,rotorliu/eigen,madlib/eigen_backup,madlib/eigen_backup,mjbshaw/Eigen,mjbshaw/Eigen,rotorliu/eigen,rotorliu/eigen,mjbshaw/Eigen,mjbshaw/Eigen,rotorliu/eigen