Quartus Streaming Softsign (PR #585 contd.)

[bo3z]

Description

• PR Softsign optimization #585 introduced an optimization for Softsign activation in the Quartus backend in io_parallel
• To ensure correct funcionality and all tests passing, this PR adds the streaming equivalent.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.B