arm: omap: usb: cleanup ehci and ohci resources and devices

The prototype and defination of functions usb_ehci_init and
usb_ohci_init are removed. The ehci and ohci devices are
removed since usbhs device contains both ehci and ohci details.

Signed-off-by: Keshava Munegowda <keshava_mgowda@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>