ARM: OMAP: USBHOST: Replace usbhs core driver APIs by Runtime pm APIs

The ehci and ohci drivers does not use the APIs of the usbhs
core driver; the runtime pm APIs are used for clock
enable/disable. Since usbhs is parent platform device of the
ehci and ohci devices, the runtime apis indirectly uses the
usb hs core device as input parameter to for clock functions.

Signed-off-by: Keshava Munegowda <keshava_mgowda@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Reviewed-by: Partha Basak <parthab@india.ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul Walmsley <paul@pwsan.com>