arm64: zynqmp: Add support for DLC21 (Smartlynq+) board

DLC21 is used as fast jtag cable. The patch adds support for this board
from PS perspective. The most interesting part on the board is seps525 oled
display. Also i2c, gpio, ethernet, uart, SD and eMMC are tested.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/3d35cd6a11cffc7456e21a88b214cc965734e852.1634231268.git.michal.simek@xilinx.com