Use SV48 when possible

[abejgonzalez]

Default to using SV48 for 64b designs. Otherwise, adhere to the RC default (SV32).

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[abejgonzalez]

This was tested in a CY/FS setup on both BOOM and Rocket default designs (booting Linux - buildroot + Ubuntu).

[tymcauley]

Just curious, what's the motivation behind this change? Working on designs with more than 512 GiB of virtual address space?

[abejgonzalez]

Just curious, what's the motivation behind this change? Working on designs with more than 512 GiB of virtual address space?

Some projects here in Berkeley are using open-source code that uses SV48 as a default (for example: https://github.com/google/tcmalloc/blob/5ed309d3de0c647a91bb41b2be68603c39aef452/tcmalloc/internal/config.h#L135). So this is just matching the default VA space to those applications (since I think it's fairly innocuous to add more space).