feat: Make USB controller configurable (#386)

src/boot.sh

@@ -22,6 +22,7 @@ case "${BOOT_MODE,,}" in
     VARS="OVMF_VARS_4M.ms.fd"
     ;;
   windows_legacy)
+    USB="usb-ehci"
     BOOT_OPTS=""
     ;;
   legacy)

src/config.sh

@@ -1,13 +1,14 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
+: "${USB:="qemu-xhci"}"
 : "${SERIAL:="mon:stdio"}"
 : "${MONITOR:="telnet:localhost:7100,server,nowait,nodelay"}"
 
 DEF_OPTS="-nodefaults"
 SERIAL_OPTS="-serial $SERIAL"
 MON_OPTS="-monitor $MONITOR"
-USB_OPTS="-device qemu-xhci -device usb-tablet"
+USB_OPTS="-device $USB -device usb-tablet"
 RAM_OPTS=$(echo "-m $RAM_SIZE" | sed 's/MB/M/g;s/GB/G/g;s/TB/T/g')
 CPU_OPTS="-cpu $CPU_FLAGS -smp $CPU_CORES,sockets=1,dies=1,cores=$CPU_CORES,threads=1"
 MAC_OPTS="-machine type=q35${SECURE},graphics=off,vmport=off,dump-guest-core=off,hpet=off${KVM_OPTS}"