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/generic/usb_cdc.h

@@ -21,7 +21,6 @@ int_fast8_t usb_send_ep0_progmem(const void *data, uint_fast8_t len);
 void usb_stall_ep0(void);
 void usb_set_address(uint_fast8_t addr);
 void usb_set_configure(void);
-void usb_request_bootloader(void);
 struct usb_string_descriptor *usbserial_get_serialid(void);
 
 // usb_cdc.c