xilinx: zynqmp: synchronize firmware call return payload

Removes duplicated definition of PAYLOAD_ARG_CNT and define it in the
firmware driver. Additionally fixes payload buffer declarations without
macro usage

Signed-off-by: Ibai Erkiaga <ibai.erkiaga-elorza@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>