drivers: power: add missing MODULE_DEVICE_TABLE in keystone-reset.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: Sebastian Reichel <sebastian.reichel@collabora.com>