x86: add cpu mtrr init function definitions to mtrr.h

mtrr.h was included everywhere needed.  Fixes the following sparse
warnings.  Also, the return types in the extern definitions were
incorrect.

arch/x86/kernel/cpu/mtrr/amd.c:113:12: warning: symbol 'amd_init_mtrr' was not declared. Should it be static?
arch/x86/kernel/cpu/mtrr/cyrix.c:268:12: warning: symbol 'cyrix_init_mtrr' was not declared. Should it be static?
arch/x86/kernel/cpu/mtrr/centaur.c:218:12: warning: symbol 'centaur_init_mtrr' was not declared. Should it be static?

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/mtrr/main.c

@@ -554,10 +554,6 @@ EXPORT_SYMBOL(mtrr_del);
  * These should be called implicitly, but we can't yet until all the initcall
  * stuff is done...
  */
-extern void amd_init_mtrr(void);
-extern void cyrix_init_mtrr(void);
-extern void centaur_init_mtrr(void);
-
 static void __init init_ifs(void)
 {
 #ifndef CONFIG_X86_64

arch/x86/kernel/cpu/mtrr/mtrr.h

@@ -97,3 +97,7 @@ void mtrr_state_warn(void);
 const char *mtrr_attrib_to_str(int x);
 void mtrr_wrmsr(unsigned, unsigned, unsigned);
 
+/* CPU specific mtrr init functions */
+int amd_init_mtrr(void);
+int cyrix_init_mtrr(void);
+int centaur_init_mtrr(void);