clk: qcom: Add additional clock debugfs support

Add the clock list_registers operation which prints the register
contents of a clock. This is supported for PLL/RCG/Branch/Gate
clocks. Also add list_rate support for the RCG clock which would
list all the frequencies/rates supported by SW.

Change-Id: I3b4cf83e776750d993d53331142223109bf0862e
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>
Signed-off-by: David Dai <daidavid1@codeaurora.org>