x86: Don't enable SMP in SPL

SMP should be set up in U-Boot where possible, not SPL. Disable it in SPL.
For 64-bit U-Boot we should find a way to allow SMP operations in U-Boot,
but this is somewhat more complicated. For now that is disabled too.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>

arch/x86/include/asm/mp.h

@@ -93,7 +93,7 @@ int x86_mp_init(void);
  */
 typedef void (*mp_run_func)(void *arg);
 
-#if defined(CONFIG_SMP) && !CONFIG_IS_ENABLED(X86_64)
+#if CONFIG_IS_ENABLED(SMP) && !CONFIG_IS_ENABLED(X86_64)
 /**
  * mp_run_on_cpus() - Run a function on one or all CPUs
  *