run_archiso: add braille support

necessary for testing brltty in archiso

what's done

added two qemu parameters:

-chardev braille,id=brltty ; creates char device which connects to brlapi.

-device usb-braille,id=usbbrl,chardev=brltty ; emulates usb baum braille display which sends it's output to chardev.

scripts/run_archiso.sh

@@ -87,9 +87,11 @@ run_image() {
         -display sdl \
         -vga virtio \
         -audiodev pa,id=snd0 \
+        -chardev braille,id=brltty \
         -device ich9-intel-hda \
         -device hda-output,audiodev=snd0 \
         -device virtio-net-pci,romfile=,netdev=net0 -netdev user,id=net0 \
+        -device usb-braille,id=usbbrl,chardev=brltty \
         -machine type=q35,smm=on,accel=kvm,pcspk-audiodev=snd0 \
         -global ICH9-LPC.disable_s3=1 \
         -enable-kvm \