Bound shape inferencer: fix int8fc scale and bias
Summary:
Previous when inferring Int8FC, we failed to carry over the scale and zero point properly.
Also fixed int8 FC weight data type to be int8 instead of uint8 as that's what C2 actually uses.
Test Plan: Use net_runner to lower a single Int8Dequantize op. Previous scale and bias would always be 1 and 0. Now the proper value is set.
Reviewed By: yinghai
Differential Revision: D22912186
fbshipit-source-id: a6620c3493e492bdda91da73775bfc9117db12d1
