drivers: gpu: drm: xen_drm_front_drm_info is declared twice

struct xen_drm_front_drm_info has been declared.
Remove the duplicate.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210325061901.851273-1-wanjiabing@vivo.com