ARM: 8613/1: Fix the uaccess crash on PB11MPCore

ARM: 8613/1: Fix the uaccess crash on PB11MPCore

The following patch was sketched by Russell in response to my
crashes on the PB11MPCore after the patch for software-based
priviledged no access support for ARMv8.1. See this thread:
http://marc.info/?l=linux-arm-kernel&m=144051749807214&w=2

I am unsure what is going on, I suspect everyone involved in
the discussion is. I just want to repost this to get the
discussion restarted, as I still have to apply this patch
with every kernel iteration to get my PB11MPCore Realview
running.

Testing by Neil Armstrong on the Oxnas NAS has revealed that
this bug exist also on that widely deployed hardware, so
we are probably currently regressing all ARM11MPCore systems.

Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: 0bac703e02ae ("ARM: software-based priviledged-no-access support")
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>