PCI: Make DPC explicitly non-modular

This code is not being built as a module by anyone:

  drivers/pci/pcie/Kconfig:config PCIE_DPC
  drivers/pci/pcie/Kconfig:  bool "PCIe Downstream Port Containment support"

Remove uses of MODULE_DESCRIPTION(), MODULE_AUTHOR(), MODULE_LICENSE(),
etc., so that when reading the driver there is no doubt it is builtin-only.
The information is preserved in comments at the top of the file.

Note that for non-modular code, module_init() translates to
device_initcall().

[bhelgaas: changelog]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Keith Busch <keith.busch@intel.com>
CC: Mika Westerberg <mika.westerberg@linux.intel.com>