MIPS: add PMD table accounting into MIPS'pmd_alloc_one

This fixes Page Table accounting bug.

MIPS is the ONLY arch just defining __HAVE_ARCH_PMD_ALLOC_ONE alone.
Since commit b2b29d6d (mm: account PMD tables like PTE tables),
"pmd_free" in asm-generic with PMD table accounting and "pmd_alloc_one"
in MIPS without PMD table accounting causes PageTable accounting number
negative, which read by global_zone_page_state(), always returns 0.
Signed-off-by: Huang Pei <huangpei@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/pgalloc.h

@@ -59,11 +59,15 @@ do {							\
 
 static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
 {
-	pmd_t *pmd;
+	pmd_t *pmd = NULL;
+	struct page *pg;
 
-	pmd = (pmd_t *) __get_free_pages(GFP_KERNEL, PMD_ORDER);
-	if (pmd)
+	pg = alloc_pages(GFP_KERNEL | __GFP_ACCOUNT, PMD_ORDER);
+	if (pg) {
+		pgtable_pmd_page_ctor(pg);
+		pmd = (pmd_t *)page_address(pg);
 		pmd_init((unsigned long)pmd, (unsigned long)invalid_pte_table);
+	}
 	return pmd;
 }