mips: Make pmd_pfn() available in all configurations

Whether or not the platform supports PMD sized pages, we need to
provide pmd_pfn() for an upcoming patch.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

arch/mips/include/asm/pgtable.h

@@ -86,6 +86,11 @@ extern void paging_init(void);
  */
 #define pmd_phys(pmd)		virt_to_phys((void *)pmd_val(pmd))
 
+static inline unsigned long pmd_pfn(pmd_t pmd)
+{
+	return pmd_val(pmd) >> _PFN_SHIFT;
+}
+
 #ifndef CONFIG_MIPS_HUGE_TLB_SUPPORT
 #define pmd_page(pmd)		(pfn_to_page(pmd_phys(pmd) >> PAGE_SHIFT))
 #endif /* CONFIG_MIPS_HUGE_TLB_SUPPORT */
@@ -422,11 +427,6 @@ static inline int pmd_write(pmd_t pmd)
 	return !!(pmd_val(pmd) & _PAGE_WRITE);
 }
 
-static inline unsigned long pmd_pfn(pmd_t pmd)
-{
-	return pmd_val(pmd) >> _PFN_SHIFT;
-}
-
 static inline struct page *pmd_page(pmd_t pmd)
 {
 	if (pmd_val(pmd) & _PAGE_HUGE)