drivers: gpu: add missing MODULE_DEVICE_TABLE in anx7625.c

This patch adds missing MODULE_DEVICE_TABLE definition which generates
correct modalias for automatic loading of this driver when it is built
as an external module.

Signed-off-by: Yu Jiahua <yujiahua1@huawei.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210616034448.34919-1-yujiahua1@huawei.com