x86: Don't include asm/u-boot.h in common

With a small fixup to u-boot-x86.h, this is not actually needed anywhere,
so drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/include/asm/u-boot-x86.h b/arch/x86/include/asm/u-boot-x86.h
index d55455f..187fe5f 100644
--- a/arch/x86/include/asm/u-boot-x86.h
+++ b/arch/x86/include/asm/u-boot-x86.h
@@ -8,13 +8,15 @@
 #ifndef _U_BOOT_I386_H_
 #define _U_BOOT_I386_H_	1
 
+struct global_data;
+
 extern char gdt_rom[];
 
 /* cpu/.../cpu.c */
 int arch_cpu_init(void);
 int x86_cpu_init_f(void);
 int cpu_init_f(void);
-void setup_gdt(gd_t *id, u64 *gdt_addr);
+void setup_gdt(struct global_data *id, u64 *gdt_addr);
 /*
  * Setup FSP execution environment GDT to use the one we used in
  * arch/x86/cpu/start16.S and reload the segment registers.