usb: extract ST USB FS peripheral core. [BREAKING CHANGE]

The breaking changes here changes in header location, and changes in driver
name passed down to the usb stack.

Changes affect: stm32f102/f103, stm32l1, and some f3 parts

* instead of the confusingly generic "usb" use the name "st_usbfs" for the USB
  Full speed peripheral ST provides in a variety of their stm32 products.
  Include directives should change as:
      #include <libopencm3/stm32/usb.h> => <libopencm3/stm32/st_usbfs.h>

* instead of the confusingly specific "f103" name for the driver, use
  "st_usbfs_v1"  [BREAKING_CHANGE]

  Instead of:
    usbd_init(&stm32f103_usb_driver, .....) ==>
    usbd_init(&st_usbfs_v1_usb_driver, .....) ==>

The purpose of these changes is to reduce some confusion around naming, but
primarily to prepare for the "v2" peripheral available on stm32f0/l0 and some
f3 devices.

Work by Frantisek Burian, Kuldeep Singh Dhaka, Robin Kreis, fenugrec and zyp
on irc, and all those forgotten.

include/libopencm3/stm32/l1/st_usbfs.h

@@ -0,0 +1,27 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/* THIS FILE SHOULD NOT BE INCLUDED DIRECTLY !
+ * Use top-level <libopencm3/stm32/st_usbfs.h>
+ */
+
+#ifndef LIBOPENCM3_ST_USBFS_H
+#	error Do not include directly !
+#else
+
+#include <libopencm3/stm32/common/st_usbfs_v1.h>
+
+#endif