[Bazel] Add support for s390x build target

While executing the test suite for Tensorflow(v2.8.0), we encountered multiple TC failures with the below error
```
'z14' is not a recognized processor for this target
```
This patch adds the s390x target to the build target list. It fixes TC failures in multiple modules of Tensorflow on s390x arch. It is also tested to have no effect on x86 machines.

Reviewed By: GMNGeoffrey

Differential Revision: https://reviews.llvm.org/D125096