arm64: zynqmp: Change compatible strings for cadence uart

Based on Linux kernel DT binding there should be different compatible
strings used that's why align zynqmp.dtsi with it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/e2404ccd22fd97fe6020be0b3b6eb3c8677f55b0.1642160583.git.michal.simek@xilinx.com