PCI: kirin: Move the power-off code to a common routine

PCI: kirin: Move the power-off code to a common routine

Instead of having two copies of the same logic, place the power-off logic
in a separate function.

No functional changes.

Link: https://lore.kernel.org/r/64f6e8da3e5fff38b6c8fcb208ace46efe6555bb.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>