make Int8 FC bias quantization use round flush to infinity
Summary:
the current quantization rounding function uses fbgemm which
defaults to round to nearest. The current implementation of hw uses round
flush to infinity. Adding such an option to switch the mode of rounding.
Test Plan: ran against test_fc_int8
Reviewed By: venkatacrc
Differential Revision: D22452306
fbshipit-source-id: d2a1fbfc695612fe07caaf84f52669643507cc9c
