x86: Explicitly include required header files.

After an experimental cleanup of <linux/percpu.h>, these files were
exposed as invoking kmalloc() without including <linux/slab.h>.
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/nmi_32.c

@@ -22,6 +22,7 @@
 #include <linux/cpumask.h>
 #include <linux/kernel_stat.h>
 #include <linux/kdebug.h>
+#include <linux/slab.h>
 
 #include <asm/smp.h>
 #include <asm/nmi.h>

arch/x86/kernel/test_nx.c

@@ -11,6 +11,8 @@
  */
 #include <linux/module.h>
 #include <linux/sort.h>
+#include <linux/slab.h>
+
 #include <asm/uaccess.h>
 #include <asm/asm.h>