selftests: riscv: test ptrace vector interface

selftests: riscv: test ptrace vector interface

Add a test case to check ptrace behavior in the case when vector
extension is supported by the system, but vector context is not
yet enabled for the traced process.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Reviewed-by: Andy Chiu <andybnac@gmail.com>
Tested-by: Andy Chiu <andybnac@gmail.com>
Link: https://patch.msgid.link/20251214163537.1054292-6-geomatsi@gmail.com
[pjw@kernel.org: dropped duplicate sys/wait.h include]
Signed-off-by: Paul Walmsley <pjw@kernel.org>