drivers:usb:fsl:Make fsl ehci drv an independent driver module

Make Freescale EHCI driver an independent entity from ehci-hcd.c.
This involves
	- using module_init/module_exit functions
	- using overrides structure
	- some necessary code cleanup

Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>