usb_cdc: Rename usb_request_bootloader() to bootloader_request()

Rename this board API function to a more generic name.  This is in
preparation for calling the function from the canbus code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/lpc176x/usbserial.c

@@ -247,7 +247,7 @@ usb_set_configure(void)
 }
 
 void
-usb_request_bootloader(void)
+bootloader_request(void)
 {
     if (!CONFIG_SMOOTHIEWARE_BOOTLOADER)
         return;