x86: include pci.h in e820_64.c

global pci_mem_start needs a declaration. include pci.h
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/e820_64.c

@@ -19,6 +19,7 @@
 #include <linux/mm.h>
 #include <linux/suspend.h>
 #include <linux/pfn.h>
+#include <linux/pci.h>
 
 #include <asm/pgtable.h>
 #include <asm/page.h>