baremetal-helloworld: Enable RISC-V 64 port

Add support for MACHINE=qemuriscv64.

$ runqemu nographic

KERNEL: [tmp/deploy/images/qemuriscv64/baremetal-helloworld-image-qemuriscv64.bin]
MACHINE: [qemuriscv64]
FSTYPE: [bin]

runqemu - INFO - Running tmp/work/x86_64-linux/qemu-helper-native/1.0-r1/recipe-sysroot-native/usr/bin/qemu-system-riscv64

Hello OpenEmbedded on RISC-V 64!

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>