PCI: Clean up build for CONFIG_PCI_QUIRKS unset

Currently, drivers/pci/quirks.c is built unconditionally, but if
CONFIG_PCI_QUIRKS is unset, the only things actually built in this
file are definitions of global variables and empty functions (due to
the #ifdef CONFIG_PCI_QUIRKS embracing all of the code inside the
file).  This is not particularly nice and if someone overlooks
the #ifdef CONFIG_PCI_QUIRKS, build errors are introduced.

To clean that up, move the definitions of the global variables in
quirks.c that are always built to pci.c, move the definitions of
the empty functions (compiled when CONFIG_PCI_QUIRKS is unset) to
headers (additionally make these functions static inline) and modify
drivers/pci/Makefile so that quirks.c is only built if
CONFIG_PCI_QUIRKS is set.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>