x86: Fix up some missing prototypes

Some functions are missing prototypes. Fix those that are specific to x86.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/interrupts.c b/arch/x86/cpu/interrupts.c
index 6f3d85f..51e2c59 100644
--- a/arch/x86/cpu/interrupts.c
+++ b/arch/x86/cpu/interrupts.c
@@ -31,7 +31,7 @@
 	"pushl $"#x"\n" \
 	"jmp irq_common_entry\n"
 
-void dump_regs(struct irq_regs *regs)
+static void dump_regs(struct irq_regs *regs)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 	unsigned long d0, d1, d2, d3, d6, d7;