topic: zynqmp: Add support for zynqmp-xilinx-xdp platform

XDP - Xilinx Drone Platform is a board for drones or other UAV.

Pinmux the SD card by default, and if the SD card detect line is high
(inactive) then pinmux the SD1 interface to EMIO instead. SD is placed on
extension card and shares connection with on board wife. That means that
when SD card is present in the board wifi can't be used.

There seems to be an issue with DDR access from PL at 2400MT/s, after
updating the PMU and ATF firmware this is causing extremely slow DDR
access. Reducing the DDR speed from 2400 to 2133 appears to solve that
issue, even though the hardware has proven to be 2400 capable.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>