tools: Optimize ring buffer for riscv

Now that the riscv tools tree supports optimized barriers, use them in
the ring buffer.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20240806-optimize_ring_buffer_read_riscv-v2-2-ca7e193ae198@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>