package/qemu: add support for RISC-V
QEMU is supported on both 32-bit and 64-bit RISC-V hosts, so let's
enable support for it in buildroot.
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>