[riscv] fence_i and amo*_w instructions
[riscv] fence_i and amo*_w instructions

cornell-brg/pydgin,cornell-brg/pydgin,cornell-brg/pydgin,futurecore/pydgin,futurecore/pydgin,cornell-brg/pydgin,futurecore/pydgin,futurecore/pydgin