clk: JSON debugfs clock tree summary

Clock information is dumped in JSON format which is easy
for machines to parse.

Each clock is represented as an object which has same name as
clock and following properties
	- enable_count
	- prepare_count
	- rate

Output is verified using online JSON editor.

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