Add register definitions for the AT91 RTC so that this can potentially be used in U-Boot. Signed-off-by: Andre Renaud <andre@designa-electronics.com> Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Heiko Schocher <hs@denx.de> Reviewed-by: Andreas Bießmann <andreas@biessmann.org>