mxc: Add generic USB HW initialization for MX51

This patch adds USB HW initializiation code to /plat-mxc/ehci.c.
	-Sets some specific PHY settings
Renames mxc_set_usbcontrol to mxc_initialize_usb_hw.
Adds new register bit defines for the USB HW on Freescale
SoCs.

This patch applies to 2.6.34-rc6.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Reviewed-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>