powerpc/mm: Drop PTE_ATOMIC_UPDATES from pmd_hugepage_update()

pmd_hugepage_update() is inside #ifdef CONFIG_TRANSPARENT_HUGEPAGE. THP
can only be enabled if PPC_BOOK3S_64=y && PPC_64K_PAGES=y, aka. hash64.

On hash64 we always define PTE_ATOMIC_UPDATES to 1, meaning the #ifdef
in pmd_hugepage_update() is unnecessary, so drop it.

That is also the only use of PTE_ATOMIC_UPDATES in any of the hash code,
meaning we no longer need to #define it at all in the hash headers.

Note it's still #defined and used in the nohash code.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/book3s/32/hash.h

@@ -39,8 +39,5 @@
 #define _PMD_PRESENT_MASK (PAGE_MASK)
 #define _PMD_BAD	(~PAGE_MASK)
 
-/* Hash table based platforms need atomic updates of the linux PTE */
-#define PTE_ATOMIC_UPDATES	1
-
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_BOOK3S_32_HASH_H */