For Juno r0, the platform reset handler needs to:
 - Implement the workaround for defect #831273
 - Increase the L2 Data and Tag RAM latencies for Cortex-A57.

Defect #831273 does not affect Juno r1. Also, the default value
for the L2 Tag RAM latency for Cortex-A57 is suitable on Juno r1.
The L2 Data RAM latency for Cortex-A57 still needs to be
increased, though.

This patch modifies the Juno platform reset handler to detect
the board revision and skip the unnecessary steps on Juno r1.
The behaviour on Juno r0 is unchanged.

Change-Id: I27542917223e680ef923ee860900806ffcd0357b