clk: zynqmp: Add clock driver support for zynqmp

Add basic clock driver support for zynqmp which
sets the required clock for GEM controller

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>