clk: qcom: Add additional clock debugfs support

Update QCOM clock debugfs to support the below functionalities.
 - Display the register contents of all the clocks which support
   this operation.
 - Display the frequency to voltage mapping of a clock.
 - Display the list of clock frequencies supported by the root
   clocks.
 - Display the clk_rate_max associated with enabled clocks list.

Also add the clock list_rate_vdd_level operation, which is required
for the "clk_enabled_list" and "trace_clocks" debugfs nodes to print
the current voltage.

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>
Signed-off-by: Mike Tipton <mdtipton@codeaurora.org>