Open-code the single use of xilinx_uartlite_create().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230220115114.25237-6-philmd@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>