perf: add qcom l2 cache perf events driver

The L2 cache perf driver is named 'l2cache_counters' and can be
used with perf tool to profile L2 cache events as below

=> DDR read (Read-Shared, Read-Unique, Read-Clean and
   Read-Not-Shared-Dirty transactions on GNOC Interface)

=> DDR write (Write-Back, Write-Clean and Write-Evict transactions
   on GNOC Interface

=> SNOOP Read (Read-Once, Read-Shared, Read-Unique, Read-Clean and
   Read-Not-Shared-Dirty transactions from GNOC to Cluster interface)

=> ACP Write(Write-Back, Write-Clean and Write-Evict transactions
   to ACP port of Collapsed Cluster)

=> Tenure counter(Low-Power mode tenure is used to count tenure (no. of XO-
   19.2MHz) of L2 Low-Power mode.

=> Low/Mid/High occurrence counter: Based on threshold set for low and mid
   tenure counter, current tenure count is compared and based on which
   category it belongs, respective occurrence counter gets incremented.
   e.g:

   1. 0 < Current Tenure <= Low-tenure threshold : Low-Tenure
   2. Low-tenure < Current Tenure <= Mid-tenure threshold : Mid-Tenure
   3. Mid-tenure < Current tenure : High-Tenure

Change-Id: I9f8aedd21a92cbd6908deb5a8e4c7e32220bea74
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>