clk: zynq: Add zynq clock framework driver

clk: zynq: Add zynq clock framework driver

Add a clock framework driver for the zynq platform. The driver is based
on the platform zynq clock driver but reworked to use static functions
instead of run-time generated objects even for unused clocks.
Additionally the CONFIG_ZYNQ_PS_CLK_FREQ is replaced by the
ps-clk-frequency from the device tree.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>