MAINTAINERS: Add some RISC-V reviewers

This patch adds some active RISC-V members as reviewers to the
MAINTAINERS file.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Acked-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-Id: <20230209003308.738237-1-alistair.francis@opensource.wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

MAINTAINERS

@@ -287,6 +287,9 @@ RISC-V TCG CPUs
 M: Palmer Dabbelt <palmer@dabbelt.com>
 M: Alistair Francis <alistair.francis@wdc.com>
 M: Bin Meng <bin.meng@windriver.com>
+R: Weiwei Li <liweiwei@iscas.ac.cn>
+R: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
+R: Liu Zhiwei <zhiwei_liu@linux.alibaba.com>
 L: qemu-riscv@nongnu.org
 S: Supported
 F: target/riscv/