UPSTREAM: ARM: Remove current_mm per-cpu variable

UPSTREAM: ARM: Remove current_mm per-cpu variable

The current_mm variable was used to store the new mm between the
switch_mm() and switch_to() calls where an IPI to reset the context
could have set the wrong mm. Since the interrupts are disabled during
context switch, there is no need for this variable, current->active_mm
already points to the current mm when interrupts are re-enabled.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Tested-by: Marc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit e323969ccda2d69f02e047c08b03faa09215c72a)

BUG=chromium-os:34007
TEST=generic system testing

Change-Id: I3ba9043520e275d593526f97aa2ecdd877effa4a
Signed-off-by: Olof Johansson <olofj@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/31852
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>