USB: ohci: move ohci_pci_{suspend,resume} to ohci-hcd.c

As suggested by Alan Stern, move the ohci-pci.c ohci_pci_{suspend,resume}
routines to ohci-hcd.c. Due to their move, also rename them to
ohci_{suspend,resume} to make it clear they operate on ohci_hcd. Since they
are not necessarily called, annotate them with __maybe_unused, and make them
enclosed within an #ifdef CONFIG_PM / #endif section.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>