Merge from x86-smp: implement SMP for both 32 and 64bit x86

A large pile of changes to the PC platform and x86 architecture that
facilitate SMP support. Tested in both 64 and 32bit on qemu and real
hardware all the way back through i486.

scripts/do-qemux86

@@ -86,7 +86,7 @@ fi
 
 ARGS=""
 if (( $DO_KVM )); then
-    ARGS+=" -enable-kvm -cpu host"
+    ARGS+=" -accel kvm -cpu host"
 else
     ARGS+=" -cpu $CPU"
 fi