usb: gadget: udc: atmel: Update endpoint allocation scheme

This patch updates the usb endpoint allocation scheme for atmel usba
driver to make sure all endpoints are allocated in order. This
requirement comes from the datasheet of the controller.

The allocation scheme is decided by fifo_mode parameter. For fifo_mode =
0 the driver tries to autoconfigure the endpoints fifo size. All other
modes contain fixed configurations optimized for different purposes. The
idea is somehow similar with the approach used on musb driver.

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>