MFD: OMAP: USB: Runtime PM support

The usbhs core driver does not enable/disable the interface and
functional clocks directly, These clocks are handled by runtime pm,
hence instead of the clock enable/disable, the runtime pm APIS are
used. however,the optional clocks and port clocks are handled by
the usbhs core.

Dependency:
This patch is dependent on this series:
[PATCH 0/5 v13 or latest version] omap: usb: host: Runtime PM preparation
for EHCI and OHCI drivers.

Validation performed:
The global suspend/resume of EHCI and OHCI is validated on
OMAP3430 sdp board with this patch combined with the series:
[PATCH 0/5 v13 or latest version] omap: usb: host: Runtime PM preparation
for EHCI and OHCI drivers.
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: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>