Perf: Add legacy support for userspace tools

We used the "rs" and "rm" modifiers to access
the L2CC and busmon PMU's before v3.4.

This patch modifies the CFG to keep the backward
compat alive till all tools progress to the
new named PMU interfaces.

Change-Id: I3a36ff8fb588382d445728a69ba790189e73ec40
Signed-off-by: Ashwin Chaugule <ashwinc@codeaurora.org>