[HW] Optimize addrgen for OS-on operation

[mp-17]

Enable OS by default and optimize addrgen critical paths.

Most of the addrgen critical quantities are calculated in advance with the least dependencies possible.

For example, the expensive computation to find the AXI end address should not depend on the mmu_valid_i signal from CVA6, i.e., the virtual address computation should not depend on CVA6's answer.

The new address can be computed ahead of time and saved as "next request" as soon as CVA6 answers back with the previous physical address, while the old virtual address is kept constant with the translation request.

Changelog

Changed

• Optimize addrgen for OS-on operation
• Enable OS by default

Checklist

• Automated tests pass
• It works on FPGA
• Changelog updated
• Code style guideline is observed
• Fix fof_exception red signal in addrgen