x86, mce: fix build failure in arch/x86/kernel/cpu/mcheck/threshold.c

Impact: build fix

The APIC code rewrite in the x86 tree broke the x86/mce branch:

 arch/x86/kernel/cpu/mcheck/threshold.c: In function ‘mce_threshold_interrupt’:
 arch/x86/kernel/cpu/mcheck/threshold.c:24: error: implicit declaration of function ‘ack_APIC_irq’

Also tidy up the file a bit while at it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/mcheck/threshold.c

-/* Common corrected MCE threshold handler code */
-#include <linux/kernel.h>
+/*
+ * Common corrected MCE threshold handler code:
+ */
 #include <linux/interrupt.h>
-#include <asm/mce.h>
+#include <linux/kernel.h>
+
 #include <asm/irq_vectors.h>
+#include <asm/apic.h>
 #include <asm/idle.h>
+#include <asm/mce.h>
 
 static void default_threshold_interrupt(void)
 {