Add some entropy to the icount timer.

So that CheriBSD doesn't hang collecting entropy we add 4 bits of
the host clock to the lower bits of the counter this is used for
the timer.

qemu-timer.c

@@ -565,7 +565,7 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
     default:
     case QEMU_CLOCK_VIRTUAL:
         if (use_icount) {
-            return cpu_get_icount();
+            return (cpu_get_icount() << 4) | (cpu_get_clock() & 0xful);
         } else {
             return cpu_get_clock();
         }