arm64: zynqmp: Use zynqmp specific compatible string for macb

The patch
"devicetree: Add compatible string for Zynq Ultrascale+ MPSoC"
(commit <988d6f07>)
introduced specific compatible string for ZynqMP which should be used
first.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>