x86: edison: Use dwc3-generic driver for Intel Edison

Use generic Synopsys DesignWare 3 driver on Intel Edison.
For now it's just a stub which allows future refactoring.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>