target/riscv: Add MXLEN check for F/D/Q applies to zama16b

target/riscv: Add MXLEN check for F/D/Q applies to zama16b

Zama16b loads and stores of no more than MXLEN bits defined in the F, D, and Q
extensions.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240802072417.659-3-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>