mips: fix build when "48 bits virtual memory" is enabled

With CONFIG_MIPS_VA_BITS_48=y the build fails miserably:

  CC      arch/mips/kernel/asm-offsets.s
In file included from arch/mips/include/asm/pgtable.h:644,
                 from include/linux/mm.h:99,
                 from arch/mips/kernel/asm-offsets.c:15:
include/asm-generic/pgtable.h:16:2: error: #error CONFIG_PGTABLE_LEVELS is not consistent with __PAGETABLE_{P4D,PUD,PMD}_FOLDED
 #error CONFIG_PGTABLE_LEVELS is not consistent with __PAGETABLE_{P4D,PUD,PMD}_FOLDED
  ^~~~~
include/asm-generic/pgtable.h:390:28: error: unknown type name 'p4d_t'; did you mean 'pmd_t'?
 static inline int p4d_same(p4d_t p4d_a, p4d_t p4d_b)
                            ^~~~~
                            pmd_t

[ ... more such errors ... ]

scripts/Makefile.build:99: recipe for target 'arch/mips/kernel/asm-offsets.s' failed
make[2]: *** [arch/mips/kernel/asm-offsets.s] Error 1

This happens because when CONFIG_MIPS_VA_BITS_48 enables 4th level of the
page tables, but neither pgtable-nop4d.h nor 5level-fixup.h are included to
cope with the 5th level.

Replace #ifdef conditions around includes of the pgtable-nop{m,u}d.h with
explicit CONFIG_PGTABLE_LEVELS and add include of 5level-fixup.h for the
case when CONFIG_PGTABLE_LEVELS==4
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: Mike Rapoport <rppt@kernel.org>

arch/mips/include/asm/pgtable-64.h

@@ -18,10 +18,12 @@
 #include <asm/fixmap.h>
 
 #define __ARCH_USE_5LEVEL_HACK
-#if defined(CONFIG_PAGE_SIZE_64KB) && !defined(CONFIG_MIPS_VA_BITS_48)
+#if CONFIG_PGTABLE_LEVELS == 2
 #include <asm-generic/pgtable-nopmd.h>
-#elif !(defined(CONFIG_PAGE_SIZE_4KB) && defined(CONFIG_MIPS_VA_BITS_48))
+#elif CONFIG_PGTABLE_LEVELS == 3
 #include <asm-generic/pgtable-nopud.h>
+#else
+#include <asm-generic/5level-fixup.h>
 #endif
 
 /*
@@ -216,6 +218,9 @@ static inline unsigned long pgd_page_vaddr(pgd_t pgd)
 	return pgd_val(pgd);
 }
 
+#define pgd_phys(pgd)		virt_to_phys((void *)pgd_val(pgd))
+#define pgd_page(pgd)		(pfn_to_page(pgd_phys(pgd) >> PAGE_SHIFT))
+
 static inline pud_t *pud_offset(pgd_t *pgd, unsigned long address)
 {
 	return (pud_t *)pgd_page_vaddr(*pgd) + pud_index(address);