PCI: Remove DPC tristate module option

Change the Downstream Port Containment config type from tristate to bool.

The driver doesn't automatically load based on any rules, so it needs to be
built-in in order to bind to devices it needs to drive.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pcie/Kconfig

@@ -83,7 +83,7 @@ config PCIE_PME
 	depends on PCIEPORTBUS && PM
 
 config PCIE_DPC
-	tristate "PCIe Downstream Port Containment support"
+	bool "PCIe Downstream Port Containment support"
 	depends on PCIEPORTBUS
 	default n
 	help
@@ -92,6 +92,3 @@ config PCIE_DPC
 	  will be handled by the DPC driver.  If your system doesn't
 	  have this capability or you do not want to use this feature,
 	  it is safe to answer N.
-
-	  To compile this driver as a module, choose M here: the module
-	  will be called pcie-dpc.