drivers: rtc: resolve year 2038 problem in rtc_to_tm

Our implementation of rtc_to_tm() cannot handle dates of more than
0x7fffffff seconds after 1970-01-01.

Adopt the Linux kernel implementation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 09f2b08..513e3ff 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -8,6 +8,7 @@
 
 obj-$(CONFIG_RTC_AT91SAM9_RTT) += at91sam9_rtt.o
 obj-y += date.o
+obj-y += rtc-lib.o
 obj-$(CONFIG_RTC_DAVINCI) += davinci.o
 obj-$(CONFIG_RTC_DS1302) += ds1302.o
 obj-$(CONFIG_RTC_DS1306) += ds1306.o