MIPS: mm: Use the TLBINVF instruction to flush the VTLB

The TLBINVF instruction can be used to flush the entire VTLB.
This eliminates the need for the TLBWI loop and improves performance.

Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6138/