x86: early_printk.c - fix pgtable.h unification fallout

 arch/x86/kernel/early_printk.c: In function ‘early_dbgp_init’:
 arch/x86/kernel/early_printk.c:827: error: ‘PAGE_KERNEL_NOCACHE’ undeclared (first use in this function)
 arch/x86/kernel/early_printk.c:827: error: (Each undeclared identifier is reported only once
 arch/x86/kernel/early_printk.c:827: error: for each function it appears in.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/early_printk.c

@@ -14,6 +14,7 @@
 #include <xen/hvc-console.h>
 #include <asm/pci-direct.h>
 #include <asm/fixmap.h>
+#include <asm/pgtable.h>
 #include <linux/usb/ehci_def.h>
 
 /* Simple VGA output */