x86: Declare global_data pointer when it is used

Several files use the global_data pointer without declaring it. This works
because the declaration is currently a NOP. But still it is better to
fix this so that x86 lines up with other archs.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/x86/lib/cmd_boot.c

@@ -36,6 +36,8 @@
 #include <malloc.h>
 #include <asm/u-boot-x86.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 unsigned long do_go_exec(ulong (*entry)(int, char * const []),
 			 int argc, char * const argv[])
 {