hw/vfio/common: Include missing 'system/tcg.h' header

hw/vfio/common: Include missing 'system/tcg.h' header

Always include necessary headers explicitly, to avoid
when refactoring unrelated ones:

  hw/vfio/common.c:1176:45: error: implicit declaration of function ‘tcg_enabled’;
   1176 |                                             tcg_enabled() ? DIRTY_CLIENTS_ALL :
        |                                             ^~~~~~~~~~~

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20250307180337.14811-2-philmd@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20250311085743.21724-4-philmd@linaro.org
Signed-off-by: Cédric Le Goater <clg@redhat.com>