ARM: zynq: add clk binding support to the ttc

Add support for retrieving TTC configuration from device tree.  This
includes the ability to pull information about the driving clocks from
the of_clk bindings.

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>