x86: unify pgd_none

Impact: cleanup

Unify and demacro pgd_none.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 0ef49f3..18afcd3 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -599,6 +599,11 @@
 {
 	return (pgd_val(pgd) & ~(PTE_PFN_MASK | _PAGE_USER)) != _KERNPG_TABLE;
 }
+
+static inline int pgd_none(pgd_t pgd)
+{
+	return !pgd_val(pgd);
+}
 #endif	/* PAGETABLE_LEVELS > 3 */
 
 #endif	/* __ASSEMBLY__ */