drm/hisilicon: Set preferred mode resolution and maximum resolution

set the preferred mode resolution to 1024 * 768 and maximum
resolution to 1920 * 1200.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Gong junjie <gongjunjie2@huawei.com>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1582080707-18825-1-git-send-email-tiantao6@hisilicon.com