arm64: add setup function for cortex-a57

arm64: add setup function for cortex-a57

The L2CTLR_EL1 register is programmed here to set correct L2
data ram latency. If it's already 2, do not write to L2CTLR_EL1.

Change-Id: I628b1b1c3a6a419a24eabc22d1b254908b276490
Signed-off-by: Bo Yan <byan@nvidia.com>
Reviewed-on: http://git-master/r/348305
Reviewed-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Tested-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Reviewed-by: Seshendra Gadagottu <sgadagottu@nvidia.com>