Add qemu-riscv@nongnu.org as the RISC-V list

We now have a RISC-V specific QEMU development list.
Reviewed-by: NAlistair Francis <alistair.francis@wdc.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

MAINTAINERS

@@ -244,6 +244,7 @@ M: Palmer Dabbelt <palmer@sifive.com>
 M: Alistair Francis <Alistair.Francis@wdc.com>
 M: Sagar Karandikar <sagark@eecs.berkeley.edu>
 M: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
+L: qemu-riscv@nongnu.org
 S: Maintained
 F: target/riscv/
 F: hw/riscv/