clk: qcom: Add support for debugfs measure clock

Introduce the clk_debug_mux which would support clock
frequency measurement from debugfs.

Change-Id: I81c32a876b33f5a7773485a76897ff9cbed45a76
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>
Signed-off-by: David Dai <daidavid1@codeaurora.org>