usb: Add driver/usb/core/(port.c,hub.h) files

This patch is to create driver/usb/core/(port.c,hub.h) files and move usb
port related code into port.c.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>