Modify LinearAPoT matrix multiplication bitshift to support all k (#82409)
### Summary
This PR modifies the bitshift implementation of matrix multiplication for LinearAPoT in `bitshift_mul` to support all input values of k. It also fixes the row/col dimension assignment for the `mat_mul `method
### Test Plan
Run unit tests with: `python test/quantization/core/experimental/test_linear.py`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82409
Approved by: https://github.com/dzdang
