MIPS: Usage and cosmetic cleanups of page table bits.

* Clean up white spaces and tabs.
   * Get rid of remaining hardcoded values for calculating
     shifts and masks.
   * Get rid of redundant macro values.
   * Do not use page table bits directly in #ifdef's.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9287/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>