MIPS: TLB support for hugetlbfs.

The TLB handlers need to check for huge pages and give them special
handling.  Huge pages consist of two contiguous sub-pages of physical
memory.

* Loading entrylo0 and entrylo1 need to be handled specially.

* The page mask must be set for huge pages and then restored after
  writing the TLB entries.

* The PTE for huge pages resides in the PMD, we halt traversal of the
  tables there.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>