drm/hisilicon/hibmc: refactored struct hibmc_drm_private

drm/hisilicon/hibmc: refactored struct hibmc_drm_private

Refactored struct hibmc_drm_private to separate VGA module from
generic struct.

Signed-off-by: Baihan Li <libaihan@huawei.com>
Signed-off-by: Yongbang Shi <shiyongbang@huawei.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250103093824.1963816-5-shiyongbang@huawei.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>