Add driver for the ST M41T94 SPI RTC

This RTC is used in some Calao boards. The driver code is taken from
the linux rtc-m41t94 driver

Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 822dc1a..ea7d899 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -44,6 +44,7 @@
 COBJS-$(CONFIG_RTC_M41T11) += m41t11.o
 COBJS-$(CONFIG_RTC_M41T60) += m41t60.o
 COBJS-$(CONFIG_RTC_M41T62) += m41t62.o
+COBJS-$(CONFIG_RTC_M41T94) += m41t94.o
 COBJS-$(CONFIG_RTC_M48T35A) += m48t35ax.o
 COBJS-$(CONFIG_RTC_MAX6900) += max6900.o
 COBJS-$(CONFIG_RTC_MC13783) += mc13783-rtc.o