mips: expose number of page table levels on Kconfig level

We would want to use number of page table level to define mm_struct.
Let's expose it as CONFIG_PGTABLE_LEVELS.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/mips/Kconfig

@@ -2600,6 +2600,11 @@ config STACKTRACE_SUPPORT
 	bool
 	default y
 
+config PGTABLE_LEVELS
+	int
+	default 3 if 64BIT && !PAGE_SIZE_64KB
+	default 2
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"