mm: remove unnecessary __GFP_HIGHMEM in __p*d_alloc_one_*()

__{pgd,p4d,pud,pmd,pte}_alloc_one_*() always allocate pages with GFP flag
GFP_PGTABLE_KERNEL/GFP_PGTABLE_USER. These two macros are defined as
follows:

#define GFP_PGTABLE_KERNEL (GFP_KERNEL | __GFP_ZERO)
#define GFP_PGTABLE_USER (GFP_PGTABLE_KERNEL | __GFP_ACCOUNT)

There is no __GFP_HIGHMEM in them, so we needn't to clear __GFP_HIGHMEM
explicitly.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Huacai Chen <[e-mail]>
Acked-by: Mike Rapoport (Microsoft) <[e-mail]>
Reviewed-by: Vishal Moola (Oracle) <[e-mail]>
Reviewed-by: Anshuman Khandual <[e-mail]>
Reviewed-by: Kevin Brodsky <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Jan Kara <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/asm-generic/pgalloc.h

···
  */
 static inline pte_t *__pte_alloc_one_kernel_noprof(struct mm_struct *mm)
 {
-	struct ptdesc *ptdesc = pagetable_alloc_noprof(GFP_PGTABLE_KERNEL &
-			~__GFP_HIGHMEM, 0);
+	struct ptdesc *ptdesc = pagetable_alloc_noprof(GFP_PGTABLE_KERNEL, 0);
 
 	if (!ptdesc)
 		return NULL;
···
 
 	if (mm == &init_mm)
 		gfp = GFP_PGTABLE_KERNEL;
-	gfp &= ~__GFP_HIGHMEM;
 
 	ptdesc = pagetable_alloc_noprof(gfp, 0);
 	if (!ptdesc)
···
 
 	if (mm == &init_mm)
 		gfp = GFP_PGTABLE_KERNEL;
-	gfp &= ~__GFP_HIGHMEM;
 
 	ptdesc = pagetable_alloc_noprof(gfp, 0);
 	if (!ptdesc)
···
 
 	if (mm == &init_mm)
 		gfp = GFP_PGTABLE_KERNEL;
-	gfp &= ~__GFP_HIGHMEM;
 
 	ptdesc = pagetable_alloc_noprof(gfp, order);
 	if (!ptdesc)