msm: clock-debug: Add support to show all the enabled clocks

Add a new debugfs file <debugfs>/clk/enabled_clocks to show all the
currently enabled clock, their rate and their dependency chain.

Example output:
cat /sys/kernel/debug/clk/enabled_clocks
Enabled clocks:
        gcc_lpass_q6_axi_clk:1:1 [0]
        gcc_mss_q6_bimc_axi_clk:1:1 [0]
        gcc_mss_cfg_ahb_clk:1:1 [0]
        gcc_boot_rom_ahb_clk:1:1 [0]
        xo_a_clk:2:2 [19200000]
        gpll0_ao:2:2 [600000000]
        kpss_ahb_clk_src:1:1 [19200000] ->
xo_a_clk:2:2 [19200000]
        bimc_msmbus_a_clk:1:1 [400000000] ->
bimc_a_clk:1:1 [400000000]
        qdss_clk:4:4 [1]
        qdss_clk:4:4 [1]
        qdss_clk:4:4 [1]
        qdss_clk:4:4 [1]
        qdss_clk:4:4 [1]
           ....
Enabled clock count: 42

Change-Id: I6eda59c7e61b77518676e3aa93895ccb792176ac
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>