drivers/ti/tps65913: Hide RTC driver from Kconfig menus

It's supposed to be selected by default on devices that ship with the
device, while there's little need to add it on other devices.

Change-Id: I57badee9ce1e8a3c8df313953aba02cc3489ff97
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40660
Reviewed-by: Michael Niewöhner
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/ti/tps65913/Kconfig

@@ -11,14 +11,9 @@
 ## GNU General Public License for more details.
 ##
 
-config DRIVERS_TI_TPS65913
-	bool "TI TPS65913 support"
-	default n
-
 config DRIVERS_TI_TPS65913_RTC
-	bool "TI TPS65913 RTC support"
+	bool
 	default n
-	select DRIVERS_TI_TPS65913
 	select RTC
 
 config DRIVERS_TI_TPS65913_RTC_BUS