rtc: Kconfig: select REGMAP_I2C when necessary

Some i2c RTC drivers are using regmap but are not selecting REGMAP_I2C
which may lead to build failures.

Link: https://lore.kernel.org/r/20200127221724.10160-2-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/Kconfig

@@ -240,6 +240,7 @@ config RTC_DRV_AS3722
 
 config RTC_DRV_DS1307
 	tristate "Dallas/Maxim DS1307/37/38/39/40/41, ST M41T00, EPSON RX-8025, ISL12057"
+	select REGMAP_I2C
 	help
 	  If you say yes here you get support for various compatible RTC
 	  chips (often with battery backup) connected with I2C. This driver
@@ -621,6 +622,7 @@ config RTC_DRV_RX8010
 
 config RTC_DRV_RX8581
 	tristate "Epson RX-8571/RX-8581"
+	select REGMAP_I2C
 	help
 	  If you say yes here you will get support for the Epson RX-8571/
 	  RX-8581.
@@ -648,6 +650,7 @@ config RTC_DRV_EM3027
 
 config RTC_DRV_RV3028
 	tristate "Micro Crystal RV3028"
+	select REGMAP_I2C
 	help
 	  If you say yes here you get support for the Micro Crystal
 	  RV3028.
@@ -677,6 +680,7 @@ config RTC_DRV_S5M
 
 config RTC_DRV_SD3078
 	tristate "ZXW Shenzhen whwave SD3078"
+	select REGMAP_I2C
 	help
 	  If you say yes here you get support for the ZXW Shenzhen whwave
 	  SD3078 RTC chips.