riscv: add HAVE_SYSCALL_TRACEPOINTS to Kconfig

I looked into Documentation/trace/ftrace-design.rst and, I think,
we check all the boxes needed for HAVE_SYSCALL_TRACEPOINTS.

Signed-off-by: David Abdurachmanov <david.abdurachmanov@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>