clk: human-readable debugfs clock tree summary

clk: human-readable debugfs clock tree summary

Adds debug file "clk_summary" in /sys/kernel/debug/clk dir.
It helps to view all the clock registered in human-readable format.

For example:
   clock                        enable_cnt  prepare_cnt  rate
---------------------------------------------------------------------
 i2s0_sync                      0           0            24000000
 spdif_in_sync                  0           0            24000000
    spdif_mux                   0           0            24000000
       spdif                    0           0            24000000
          spdif_doubler         0           0            48000000
             spdif_div          0           0            48000000
                spdif_2x        0           0            48000000
 clk_32k                        2           2            32768
    blink_override              1           1            32768
       blink                    1           1            32768
 clk_m                          2           2            12000000
    clk_out_3_mux               0           0            12000000
       clk_out_3                0           0            12000000
    pll_ref                     3           3            12000000
       pll_e_mux                0           0            12000000
          pll_e                 0           0            100000000
             cml0               0           0            100000000
             cml1               0           0            100000000
             pciex              0           0            100000000
       pll_d2                   0           0            1000000
          pll_d2_out0           0           0            500000
       pll_d                    0           0            1000000
          pll_d_out0            0           0            500000
             dsib_mux           0           0            500000
                dsib            0           0            500000
             dsia               0           0            500000

Signed-off-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>