Add support for Zdinx extension

[anuani21]

#DEVELOPMENT PRs SHOULD BE TO DEV BRANCH ONLY

Description

• Added cover group format for RV32Zdinx instructions.
• Added cover group format for RV64Zdinx instructions.
• Introduced ZDINX flag to aid the compilation of double precision floating ops into integer regs.
• For RV32Zdinx, we use the pair register to accommodate 64 bit value.

Related Issues

NA

Update to/for Ratified/Unratified Extensions or to framework

• Ratified

List Extensions

- Zdinx

[jamesbeyond]

Dear @anuani21

The CTG and ISAC Repo had been moved to riscv-arch-test via PR
riscv/riscv-arch-test#495

If you think this PR is important, and need to me merged on to risc-v CTG or ISAC, please re-submit your PR against riscv-arch-test

This repository shall be archived in about one week time .