hw/mips/loongson3_virt: Include 'system/system.h'

Files using serial_hd() should include 'system/system.h'. Fix that.

Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250901064631.530723-4-clg@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/mips/loongson3_virt.c

@@ -49,6 +49,7 @@
 #include "system/qtest.h"
 #include "system/reset.h"
 #include "system/runstate.h"
+#include "system/system.h"
 #include "qemu/error-report.h"
 
 #define PM_CNTL_MODE          0x10