usb: gadget: pch_udc: enable MSI if hardware supports

Try to enable MSI in case hardware supports it. At least Intel Quark is
known SoC which indeed does.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>