nds32: use pgtable-nopmd instead of 4level-fixup

nds32 has only two-level page tables and can use pgtable-nopmd and
folding of the upper layers.

Replace usage of include/asm-generic/4level-fixup.h and explicit
definition of __PAGETABLE_PMD_FOLDED in nds32 with
include/asm-generic/pgtable-nopmd.h and adjust page table manipulation
macros and functions accordingly.

Link: http://lkml.kernel.org/r/1572938135-31886-8-git-send-email-rppt@kernel.org


Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Anatoly Pugachev <matorola@gmail.com>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Mark Salter <msalter@redhat.com>
Cc: Matt...