RISC-V: Add Xuantie extensions for xt-c930

The extensions are as followings:

1. Add xtheadaioe extension
2. Add xtheadcbop extension
3. Add XTheadVarith extension
4. Add XTheadVcoder extension
5. Add XTheadVcrypto extension
6. Add XTheadVdot extension
7. Add XTheadVsfa extension
8. Add XTheadVsfb extension