fpga: zynq: Add support for loading bitstream

Devcfg device requires to load bitstream in binary format.
But u-boot also has an option for loading bitstream in bit
format. Let's handle both cases by zynqpl driver.
Also add suport for loading partial bitstreams.

The first driver version was done by:
Joe Hershberger <joe.hershberger@ni.com>

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@ti.com>