ARM: 8391/1: l2c: add options to overwrite prefetching behavior

These options make it possible to overwrites the data and instruction
prefetching behavior of the arm pl310 cache controller.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>