ARM: nomadik: get the cache running normally

There were earlier problems with the L210 cache on the Nomadik.
It turns out that to run the cache at full speed, you need to
set the "write allocate override" bit in the auxilary control
register. Now that this bit can be set from the device tree, we
can set down the latencies to 2 again.

Cc: stable@vger.kernel.org
Fixes: a461a3ecfc7e ("ARM: nomadik: set latencies to 8 cycles")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>