ARM: 8556/1: on a generic DT system: do not touch l2x0

Set no bits, mask all bits in the AUX l2x0 register for the
default DT ARM system: if anything needs to be modified, it
should be done using DT bindings.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>