Add double buffering routines

Signed-off-by: Manuel Odendahl <wesen@ruinwesen.com>
Rename USB_EP_EP_KIND to USB_EP_EP_KIND_DBL_BUF

Signed-off-by: Manuel Odendahl <wesen@ruinwesen.com>
Refactor setting a USB EP rx count

Signed-off-by: Manuel Odendahl <wesen@ruinwesen.com>
Rename misleading ptr function

Signed-off-by: Manuel Odendahl <wesen@ruinwesen.com>
usb_reg_map.h: Fix incorrect register bit definitions.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
usb_reg_map.c: Fix incorrect function name call.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
Merge branch 'dbl-buf-usb'

For bulk double buffer support.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>