riscv: select ARCH_USE_CMPXCHG_LOCKREF

Select ARCH_USE_CMPXCHG_LOCKREF to enable the cmpxchg-based lockless
lockref implementation for riscv.

Using Linus' test case[1] on TH1520 platform, I see a 11.2% improvement.
On JH7110 platform, I see 12.0% improvement.

Link: http://marc.info/?l=linux-fsdevel&m=137782380714721&w=4

 [1]
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20240325111038.1700-2-jszhang@kernel.org


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