usb: host: omap: common usb host core driver

enabling and disabling the common clocks for ehci
and ohci is implemented. usbhs is a common parent
platform driver for EHCI and OHCI driver. This driver
receives the clock enable and disable requests
from ehci and ohci drivers.The UHH and TLL
initialization is also performed.

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