rename fast_conv_bn_eval to efficient_conv_bn_eval

[youkaichao]

Motivation

The name fast_conv_bn_eval is not representative. Rename to efficient_conv_bn_eval.

Modification

Feature rename.

BC-breaking (Optional)

N/A

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.