x86, espfix: Move espfix definitions into a separate header file

Sparse warns that the percpu variables aren't declared before they are
defined.  Rather than hacking around it, move espfix definitions into
a proper header file.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/espfix.h

+#ifdef _ASM_X86_ESPFIX_H
+#define _ASM_X86_ESPFIX_H
+
+#ifdef CONFIG_X86_64
+
+#include <asm/percpu.h>
+
+DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
+DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
+
+extern void init_espfix_bsp(void);
+extern void init_espfix_ap(void);
+
+#endif /* CONFIG_X86_64 */
+
+#endif /* _ASM_X86_ESPFIX_H */

arch/x86/include/asm/setup.h

@@ -57,11 +57,10 @@ extern void x86_ce4100_early_setup(void);
 static inline void x86_ce4100_early_setup(void) { }
 #endif
 
-extern void init_espfix_bsp(void);
-extern void init_espfix_ap(void);
-
 #ifndef _SETUP
 
+#include <asm/espfix.h>
+
 /*
  * This is set up by the setup-routine at boot-time
  */

arch/x86/kernel/espfix_64.c

@@ -40,6 +40,7 @@
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/setup.h>
+#include <asm/espfix.h>
 
 /*
  * Note: we only need 6*8 = 48 bytes for the espfix stack, but round