usb: host: omap: ehci and ohci simplification

The ehci and ohci drivers are simplified; Since
UHH and TLL initialization, clock handling are
done by common usbhs core driver, these functionalities
are removed from ehci and ohci drivers.

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