usb: Add support for EP0-OUT-only ping-pong mode (mode 1)
usb: Add support for EP0-OUT-only ping-pong mode (mode 1)

1. Use PPB_EP0_OUT and PPB_EP0_IN defines instead of PPB_EP0.
2. Add BDS*() macros for this ping-pong mode.
3. Add EP_BUF() macros for this ping-pong mode.
4. Add buffer pointers to ep0_buf{} struct.
5. Use SFR_USB_STATUS_PPBI register bit to determine which buffer or
   buffer descriptor to use for all accesses.

Basic defines and structure related to ping-pong mode 2 (full ping-pong)
are also included in this patch.

rollingstone/m-stack,pololu/m-stack,pololu/m-stack,rollingstone/m-stack