[xnnpack] Improve qd8-f16 testing

Pull Request resolved: #7745

* Added a few qd8 fp16 tests for qc4w and qc8w
* Cleaned up and split fp16 and fp32 for basic tests to avoid getting confused regarding atol issues
* Created a TODO to look into atol values
ghstack-source-id: 262438488
@exported-using-ghexport

Differential Revision: [D68350952](https://our.internmc.facebook.com/intern/diff/D68350952/)

Author: digantdesai