The current compile-time check for inversed IENB/CNTL does not
work in multiplatform boots: as soon as versatile is included
in the build, the IENB/CNTL is switched and breaks graphics.
Convert this to a runtime switch.

Cc: stable@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Fixes: a29da136 ("ARM: versatile: convert to multi-platform")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>