x86/PCI: Replace deprecated EXTRA_CFLAGS with ccflags-y

Update arch/x86/pci/Makefile replacing the deprecated EXTRA_CFLAGS with the
ccflags-y matching recommendation per section 3.7 of
Documentation/kbuild/makefiles.txt.

Link: https://lore.kernel.org/r/20190819060532.17093-1-kw@linux.com


Signed-off-by: Krzysztof Wilczynski <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>