arm64: zynqmp: Add new uartps compatible string

Mainline kernel has r1p12 compatible string now. Use this new compatible
string and also append generic compatible string.
Keep in your mind that using this generic compatible string not all uart
features will be available.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Moritz Fischer <mdf@kernel.org>