USB: gadget: Separate out PCI bus code from ci13xxx_udc

Move PCI bus code from ci13xxx_udc to a new file ci13xxx_pci.  SoC's
which has MIPS USB core can include the ci13xxx_udc and keep bus glue
code in their respective gadget controller drivers.

Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>