PCI: kirin: Allow building it as a module

There's nothing preventing this driver from being loaded as a module.
Change its config from bool to tristate.

Link: https://lore.kernel.org/r/b5e7cfe9df09b492750bd6db0f0c911eaae8c2d4.1634812676.git.mchehab+huawei@kernel.orgSigned-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>

drivers/pci/controller/dwc/Kconfig

@@ -266,7 +266,7 @@ config PCIE_KEEMBAY_EP
 
 config PCIE_KIRIN
 	depends on OF && (ARM64 || COMPILE_TEST)
-	bool "HiSilicon Kirin series SoCs PCIe controllers"
+	tristate "HiSilicon Kirin series SoCs PCIe controllers"
 	depends on PCI_MSI_IRQ_DOMAIN
 	select PCIE_DW_HOST
 	help