Change function names and add SIMD implementation for two c functions:
(1) var_filter_block2d_bil_first_pass
(2) var_filter_block2d_bil_second_pass

This CL allows aom_jnt_sub_pixel_avg_variance now in SIMD.

Change-Id: Ib41ef13d62ae91a0ca481bcebb24568dcd4722c4