hw/char/pl011: Warn when using disabled receiver

hw/char/pl011: Warn when using disabled receiver

We shouldn't receive characters when the full UART or its
receiver is disabled. However we don't want to break the
possibly incomplete "my first bare metal assembly program"s,
so we choose to simply display a warning when this occurs.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Luc Michel <luc.michel@amd.com>
Message-Id: <20250220092903.3726-2-philmd@linaro.org>