usb: dwc3: Rework clock initialization to be more flexible

usb: dwc3: Rework clock initialization to be more flexible

The dwc3 core binding specifies three clocks:
  ref, bus_early, and suspend

which are all controlled in the driver together.

However some variants of the hardware my not have all three
clks, or some may have more. Usually this was handled by using
the dwc3-of-simple glue driver, but that resulted in a
proliferation of bindings for for every variant, when the only
difference was the clocks and resets lists.

So this patch reworks the reading of the clks from the dts to
use devm_clk_bulk_get_all() will will fetch all the clocks
specified in the dts together.

This patch was recommended by Rob Herring <robh@kernel.org>
as an alternative to creating multiple bindings for each variant
of hardware.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
CC: ShuFan Lee <shufan_lee@richtek.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: Yu Chen <chenyu56@huawei.com>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Jun Li <lijun.kernel@gmail.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Guillaume Gardet <Guillaume.Gardet@arm.com>
Cc: Jack Pham <jackp@codeaurora.org>
Cc: linux-usb@vger.kernel.org
Cc: devicetree@vger.kernel.org
Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>