UPSTREAM: usb: dwc3: add generic OF glue layer

UPSTREAM: usb: dwc3: add generic OF glue layer

For simple platforms which merely enable some clocks
and populate its children, we can use this generic
glue layer to avoid boilerplate code duplication.

For now this supports Qcom and Xilinx, but if we
find a way to add generic handling of regulators and
optional PHYs, we can absorb exynos as well.

Tested-by: Subbaraya Sundeep Bhatta <subbaraya.sundeep.bhatta@xilinx.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
(cherry picked from commit 16adc674d0d68a50dfc725574738d7ae11cf5d7e)

Change-Id: Ia397ebcc522d0cd33c8dd3ee286dc2e0a5383a58
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>