arch-riscv: Refactor compressed instructions

1. C.JAL should use CJOp format to generate code
2. Use sext function to handle MSB for immediate
3. Add IsCall flags to c.jal, c.jalr
4. Use JumpConstructor to CJOp format

Change-Id: Id01c0d7cc1a3e17776890268879c568fc9996bc5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66732
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed