PCI: Add SPDX GPL-2.0 to replace COPYING boilerplate

Add SPDX GPL-2.0 to all PCI files that referred to the kernel default
"COPYING" file, which specifies GPL version 2.

Remove the boilerplate language referring to the GPL and "COPYING", relying
on the assertion in b2441318 ("License cleanup: add SPDX GPL-2.0
license identifier to files with no license") that the SPDX identifier may
be used instead of the full boilerplate text.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>