target/riscv: add support for zhinx/zhinxmin

target/riscv: add support for zhinx/zhinxmin

  - update extension check REQUIRE_ZHINX_OR_ZFH and REQUIRE_ZFH_OR_ZFHMIN_OR_ZHINX_OR_ZHINXMIN
  - update half float point register read/write
  - disable nanbox_h check

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>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220211043920.28981-6-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>