msm: cpufreq: Add msm_cpufreq debugfs file to show CPU -> L2/BW mapping

Example output:
cat /sys/kernel/debug/clk/msm_cpufreq
  CPU (KHz)  L2 (KHz)  Mem (MBps)
     300000    300000         600
     422400    422400        1200
     652800    499200        1600
     729600    576000        2456
     883200    576000        2456
     960000    960000        3680
    1036800   1036800        3680
    1190400   1036800        3680
    1267200   1267200        6400
    1497600   1497600        6400
    1574400   1574400        6400
    1728000   1651200        6400
    1958400   1728000        7448
    2265600   1728000        7448

Change-Id: I20df8c3778c0fcd0ef1f369acb1cb72cf5334812
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>