hw/virtio: Add missing "hw/core/cpu.h" include

hw/virtio: Add missing "hw/core/cpu.h" include

virtio.c uses target_words_bigendian() which is declared in
"hw/core/cpu.h". Add the missing header to avoid when refactoring:

  hw/virtio/virtio.c:2451:9: error: implicit declaration of function 'target_words_bigendian' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    if (target_words_bigendian()) {
        ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221213111707.34921-2-philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>