x86: cpu: Add missing header inclusion

Without asm/cpu_x86.h inclusion a compiler is not happy:

  arch/x86/cpu/cpu_x86.c:14:5: warning: no previous prototype for ‘cpu_x86_bind’ [-Wmissing-prototypes]
  arch/x86/cpu/cpu_x86.c:29:5: warning: no previous prototype for ‘cpu_x86_get_vendor’ [-Wmissing-prototypes]
  arch/x86/cpu/cpu_x86.c:41:5: warning: no previous prototype for ‘cpu_x86_get_desc’ [-Wmissing-prototypes]
  arch/x86/cpu/cpu_x86.c:55:5: warning: no previous prototype for ‘cpu_x86_get_count’ [-Wmissing-prototypes]

Add missing header inclusion.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/cpu_x86.c b/arch/x86/cpu/cpu_x86.c
index 6c53f0e..6c32ae4 100644
--- a/arch/x86/cpu/cpu_x86.c
+++ b/arch/x86/cpu/cpu_x86.c
@@ -7,6 +7,7 @@
 #include <dm.h>
 #include <errno.h>
 #include <asm/cpu.h>
+#include <asm/cpu_x86.h>
 #include <asm/global_data.h>
 
 DECLARE_GLOBAL_DATA_PTR;