PCI: kirin: Allow removing the driver

Now that everything is in place at the poweroff sequence, this driver can
use module_platform_driver(), which allows it to be removed.

Link: https://lore.kernel.org/r/53b40494252444a9b830827922c4e3a301b8f863.1634812676.git.mchehab+huawei@kernel.org


Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Xiaowei Song <songxiaowei@hisilicon.com>