x86: common.c boot_cpu_stack and boot_exception_stacks should be static

Impact: cleanup, avoid sparse warnings, reduce kernel size a bit

Fixes these sparse warnings:

 arch/x86/kernel/cpu/common.c:869:6: warning: symbol 'boot_cpu_stack' was not declared. Should it be static?
 arch/x86/kernel/cpu/common.c:910:6: warning: symbol 'boot_exception_stacks' was not declared. Should it be static?
Signed-off-by: Jaswinder Singh <jaswinder@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/common.c

@@ -862,7 +862,7 @@ EXPORT_SYMBOL(_cpu_pda);
 
 struct desc_ptr idt_descr = { 256 * 16 - 1, (unsigned long) idt_table };
 
-char boot_cpu_stack[IRQSTACKSIZE] __page_aligned_bss;
+static char boot_cpu_stack[IRQSTACKSIZE] __page_aligned_bss;
 
 void __cpuinit pda_init(int cpu)
 {
@@ -903,7 +903,7 @@ void __cpuinit pda_init(int cpu)
 	}
 }
 
-char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ +
+static char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ +
 				  DEBUG_STKSZ] __page_aligned_bss;
 
 extern asmlinkage void ignore_sysret(void);