msm: 9625: Add secure call to enable L2 cache

MSM9625 has trustzone support and L2 control registers are
not accessible from the non secure side where the linux
kernel runs. Add a smc call to enable the L2 cache from linux.
Also update the L2 initialization routine by passing a null aux
control value since it's setup by trustzone.

Change-Id: I2eee2bd41ba14adbff597e4f4903ad81d6382e14
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>