clk: gxbb: expose USB clocks

USB0_DDR_BRIDGE and USB1_DDR_BRIDGE1 are needed for the related
dwc2 usb controller. USB, USB0 and USB1 are needed for the PHYs.
Expose these clocks to DT and comment out in clk driver.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>