atusb/fw2: support device -> host side of the ATUSB EP0 protocol

- ep0.c: the ATUSB EP0 protocol engine
- Makefile (OBJS): added ep0.o
- atusb.c (main): initialize the EP0 protocol
- spi.h: whitespace cleanup

usb/patches/support-vendor-requests.patch:

- usb/ctrl.c (ctrl_handler): also pass vendor-specific requests to the
  class handler
- class/CDC/cdc.c (cdc_req_handler): reject vendor requests

atusb/fw2/spi.h

@@ -3,6 +3,7 @@
 
 #include <stdint.h>
 
+
 void spi_begin(void);
 uint8_t spi_io(uint8_t v);
 void spi_end(void);