rtc: Rename RTC_SUPPORT to RTC

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 93eff14..15ddb0d 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1073,7 +1073,7 @@
 	  Enable support for REMOTEPROCs in SPL. This permits to load
 	  a remote processor firmware in SPL.
 
-config SPL_RTC_SUPPORT
+config SPL_RTC
 	bool "Support RTC drivers"
 	help
 	  Enable RTC (Real-time Clock) support in SPL. This includes support
@@ -1562,7 +1562,7 @@
 	  be already in memory when TPL takes over, e.g. loaded by the boot
 	  ROM.
 
-config TPL_RTC_SUPPORT
+config TPL_RTC
 	bool "Support RTC drivers"
 	help
 	  Enable RTC (Real-time Clock) support in TPL. This includes support