powerpc/mm/book3s64/hash/4k: Add pmd_same callback for 4K page size

With commit 0d940a9b ("mm/pgtable: allow pte_offset_map[_lock]() to
fail") the kernel is now using pmd_same to compare pmd values that are
pointing to a level 4 page table page. Move the functions out of #ifdef
CONFIG_TRANSPARENT_HUGEPAGE and add a variant that can work with both 4K
and 64K page size.

kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:141!
Oops: Exception in kernel mode, sig: 5 [#1]
LE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
.....
NIP [c00000000048aee0] __pte_offset_map_lock+0xf0/0x164
LR [c00000000048ae78] __pte_offset_map_lock+0x88/0x164
Call Trace:
 0xc0003f000009a340 (unreliable)
 __handle_mm_fault+0x1340/0x1980
 handle_mm_fault+0xbc/0x380
 __get_user_pages+0x320/0x550
 get_user_pages_remote+0x13c/0x520
 get_arg_page+0x80/0x1d0
 copy_string_kernel+0xc8/0x250
 kernel_execve+0x11c/0x270
 run_init_process+0xe4/0x10c
 kernel_init+0xbc/0x1a0
 ret_from_kernel_user_thread+0x14/0x1c

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230706022405.798157-1-aneesh.kumar@linux.ibm.com