MIPS: Fix mips_atomic_set() with EVA

EVA linked loads (LLE) and conditional stores (SCE) should be used on
EVA kernels for the MIPS_ATOMIC_SET operation of the sysmips system
call, or else the atomic set will apply to the kernel view of the
virtual address space (potentially unmapped on EVA kernels) rather than
the user view (TLB mapped).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 3.15.x-
Patchwork: https://patchwork.linux-mips.org/patch/16151/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>