selftests: riscv: verify ptrace accepts valid vector csr values

selftests: riscv: verify ptrace accepts valid vector csr values

Add a test to v_ptrace test suite to verify that ptrace accepts the
valid input combinations of vector csr registers. Use kselftest
fixture variants to create multiple inputs for the test.

The test simulates a debug scenario with three breakpoints:
0. init: let the tracee set up its initial vector configuration
1. 1st bp:  modify the tracee's vector csr registers from the debugger
  - resume the tracee to execute a block without vector instructions
2. 2nd bp: read back the tracees's vector csr registers from the debugger
  - compare with values set by the debugger
  - resume the tracee to execute a block with vector instructions
3. 3rd bp: read back the tracess's vector csr registers again
  - compare with values set by the debugger

The last check helps to confirm that ptrace validation check for vector
csr registers input values works properly and maintains an accurate view
of the tracee's vector context in debugger.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Tested-by: Andy Chiu <andybnac@gmail.com>
Link: https://patch.msgid.link/20251214163537.1054292-10-geomatsi@gmail.com
[pjw@kernel.org: cleaned up a checkpatch issue]
Signed-off-by: Paul Walmsley <pjw@kernel.org>