sched: replace up_cpu_index with this_cpu

Make this_cpu is arch independent and up_cpu_index do that.
In AMP mode, up_cpu_index() may return the index of the physical core.

Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>

arch/arm/src/qemu/qemu_cpuboot.c

@@ -111,7 +111,7 @@ void qemu_cpu_enable(void)
  *
  * Input Parameters:
  *   cpu - The CPU index.  This is the same value that would be obtained by
- *      calling up_cpu_index();
+ *      calling this_cpu();
  *
  * Returned Value:
  *   Does not return.