target/riscv: add support for zdinx

target/riscv: add support for zdinx

  -- update extension check REQUIRE_ZDINX_OR_D
  -- update double float point register read/write

Co-authored-by: ardxwe <ardxwe@gmail.com>
Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220211043920.28981-5-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>