usb: gadget: ci13xxx: convert to platform device

Let's break ci13xxx driver into a separate udc driver and platform
drivers _pci and _msm, which will create a platform device for each pci
(or msm) device found. The approach was introduced by Felipe in dwc3
driver and there seems to be no reason not to use it.

msm related code is only compile-tested.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>