AT91: add RTT and GPBR based RTC

Signed-off-by: Reinhard Meyer <u-boot@emk-elektronik.de>
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 772a49a..98734db 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -27,6 +27,7 @@
 
 LIB	= $(obj)librtc.a
 
+COBJS-$(CONFIG_RTC_AT91SAM9_RTT) += at91sam9_rtt.o
 COBJS-$(CONFIG_RTC_BFIN) += bfin_rtc.o
 COBJS-y += date.o
 COBJS-$(CONFIG_RTC_DS12887) += ds12887.o