target/riscv: Add Zaamo and Zalrsc extension infrastructure

target/riscv: Add Zaamo and Zalrsc extension infrastructure

These extensions represent the atomic operations from A (Zaamo) and the
Load-Reserved/Store-Conditional operations from A (Zalrsc)

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240123111030.15074-2-rbradford@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>