[ARM] Convert pmd_page() to be highmem safe

In the long run, we may want to place page tables in highmem.  However,
pmd_page() has traditionally been coded to convert the physical address
to a virtual one, which won't work with highmem pages.  Instead,
translate the physical address to a PFN, and then convert the PFN to a
struct page instead.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/pgtable.h

@@ -342,7 +342,7 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd)
 	return __va(ptr);
 }
 
-#define pmd_page(pmd) virt_to_page(__va(pmd_val(pmd)))
+#define pmd_page(pmd)		pfn_to_page(__phys_to_pfn(pmd_val(pmd)))
 
 /*
  * Conversion functions: convert a page and protection to a page entry,