Feature/rv64 rvv support

[goodnorning]

PR checklist

• Updated function header with a short description and version number
• Added test case for bug fix or new feature
• Validated on real hardware

[fdesbiens]

Thank you for this contribution, @goodnorning! We will review it and come back if there is any feedback.

We are currently under code freeze before the Q1 2026 release. I will only merge to dev after the release. This feature would ship in our Q2 2026 release in June.

[akifejaz]

Hi @goodnorning

Thankyou so much for your contribution.

I liked the implementation and it looks good from myside, Here is my feedback on some minor issues.

• vstart must be restored before vsetvl. vstart is the start index for vector operations. Setting vstart AFTER vsetvl has no effect on the current vl configuration.
• saving vxrm and vxsat separately which is functionally equivalent, but vcsr should also be explicitly handled for spec compliance.
• add #ifdef __riscv_vector guard in link.lds as its silently wasting 16 KB on every non-vector build.
• the vxrm and vxsat seems swapped on restore, save stores vxrm at offset 3 and vxsat at offset 4, but every restore (csrw) writes offset 3 into vxsat and offset 4 into vxrm
• also add #ifdef __riscv_vector guard in entry.s