preempt_rt: Allow BORE cpusched on compatible kernels

It's a pretty minor CFS mod, should work 🐸

linux-tkg-config/prepare

@@ -285,8 +285,12 @@ _set_cpu_scheduler() {
   fi
 
   if [ "${_preempt_rt}" = "1" ]; then
+    if [[ "${_avail_cpu_scheds[*]}" =~ "bore" ]]; then
+      _avail_cpu_scheds=("cfs" "bore")
+    else
       _avail_cpu_scheds=("cfs")
     fi
+  fi
 
   # Populate descriptions of the available CPU schedulers
   _avail_cpu_scheds_text=()