rtc: armada38x: depend on OF

The driver will compile with warning without OF because armada38x_data and
armada8k_data will be defined but not used. It would be possible to move
then in the #ifdef CONFIG_OF section but then their members will be defined
but not used. Instead of moving most of the driver in the #ifdef, simply
depend on OF.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210202112219.3610853-3-alexandre.belloni@bootlin.com

drivers/rtc/Kconfig

@@ -1594,6 +1594,7 @@ config RTC_DRV_MV
 config RTC_DRV_ARMADA38X
 	tristate "Armada 38x Marvell SoC RTC"
 	depends on ARCH_MVEBU || COMPILE_TEST
+	depends on OF
 	help
 	  If you say yes here you will get support for the in-chip RTC
 	  that can be found in the Armada 38x Marvell's SoC device