smp: move a preprocessor conditional from .c to cmake

smp.c only has to be built if CONFIG_SMP is enabled. Remove
preprocessor checks from the file itself and update cmake rules
instead.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

kernel/CMakeLists.txt

@@ -27,10 +27,15 @@ list(APPEND kernel_files
   stack.c
   system_work_q.c
   work.c
-  smp.c
   sched.c
   condvar.c
   )
+
+if(CONFIG_SMP)
+list(APPEND kernel_files
+     smp.c)
+endif()
+
 endif()
 
 if(CONFIG_XIP)

kernel/smp.c

@@ -10,7 +10,6 @@
 #include <kswap.h>
 #include <kernel_internal.h>
 
-#ifdef CONFIG_SMP
 static atomic_t global_lock;
 static atomic_t start_flag;
 
@@ -104,5 +103,3 @@ bool z_smp_cpu_mobile(void)
 	arch_irq_unlock(k);
 	return !pinned;
 }
-
-#endif /* CONFIG_SMP */