usb: add CONFIG_USB_PCI for system have both PCI HW and non-PCI based USB HW

a lot of embeded system SOC (e.g. freescale T2080) have both
PCI and USB modules. But USB module is controlled by registers directly,
it have no relationship with PCI module.

when say N here it will not build PCI related code in USB driver.

Signed-off-by: yuan linyu <Linyu.Yuan@alcatel-sbell.com.cn>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>