usb: bdc: Add clock enable for new chips with a separate BDC clock

Newer SoC's have added a BDC clock to the Device Tree, so get
and enable it.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>