x86: ivybridge: Declare global data where it is used

Some files are missing this declaration. Add it to avoid build errors when
we actually need the declaration.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/ivybridge/model_206ax.c b/arch/x86/cpu/ivybridge/model_206ax.c
index 09b5342..d5f3219 100644
--- a/arch/x86/cpu/ivybridge/model_206ax.c
+++ b/arch/x86/cpu/ivybridge/model_206ax.c
@@ -22,6 +22,8 @@
 #include <asm/turbo.h>
 #include <asm/arch/model_206ax.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 static void enable_vmx(void)
 {
 	struct cpuid_result regs;