Regif Chead union struct name add prefix

[xiaozhulanshan]

Closes #

Context, Motivation & Description

Regif Chead union struct name will conflict in different regfile with same field name . So we add prefix in Regif Chead union struct name

Impact on code generation

Checklist

• Unit tests were added
• API changes are or will be documented:
  • using Scaladoc comments: /** */?
  • on RTD?
  • thanks to a new tracking issue on RTD?

[jijingg]

@xiaozhulanshan thanks