x86: cpu: Mark a few functions static

Some functions are not used anywhere except the same file
where they are defined. Mark them static. This helps avoiding
the compiler warnings:

  arch/x86/cpu/cpu.c:343:6: warning: no previous prototype for ‘detect_coreboot_table_at’ [-Wmissing-prototypes]
  arch/x86/cpu/mtrr.c:90:6: warning: no previous prototype for ‘mtrr_write_all’ [-Wmissing-prototypes]
  arch/x86/cpu/i386/interrupt.c:240:6: warning: no previous prototype for ‘__do_irq’ [-Wmissing-prototypes]

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/cpu/cpu.c

@@ -340,7 +340,7 @@ int reserve_arch(void)
 }
 #endif
 
-long detect_coreboot_table_at(ulong start, ulong size)
+static long detect_coreboot_table_at(ulong start, ulong size)
 {
 	u32 *ptr, *end;
 

arch/x86/cpu/i386/interrupt.c

@@ -237,7 +237,7 @@ void *x86_get_idt(void)
 	return &idt_ptr;
 }
 
-void __do_irq(int irq)
+static void __do_irq(int irq)
 {
 	printf("Unhandled IRQ : %d\n", irq);
 }

arch/x86/cpu/mtrr.c

@@ -87,7 +87,7 @@ void mtrr_read_all(struct mtrr_info *info)
 	}
 }
 
-void mtrr_write_all(struct mtrr_info *info)
+static void mtrr_write_all(struct mtrr_info *info)
 {
 	int reg_count = mtrr_get_var_count();
 	struct mtrr_state state;