hw/loongarch/virt: Remove unused ISA UART

The LoongArch 'virt' machine doesn't use any ISA UART.
No need to build the device model, remove its Kconfig entry.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20231010135342.40219-2-philmd@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
1 file changed