Faster versions of fvec_op_ny_Dx for AVX2 (#2811)

Summary:
Pull Request resolved: #2811

Use transpose_AxB kernels to speedup computations.

Reviewed By: mdouze

Differential Revision: D44726814

fbshipit-source-id: e6f07f4513b4e135b4fcae2b3f699b359784099c

Author: Alexandr Guzhva