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/configs/openpiton_riscv64_spl_defconfig b/configs/openpiton_riscv64_spl_defconfig
index 67fbcdd..5107e87 100644
--- a/configs/openpiton_riscv64_spl_defconfig
+++ b/configs/openpiton_riscv64_spl_defconfig
@@ -25,7 +25,7 @@
 # CONFIG_SPL_BANNER_PRINT is not set
 CONFIG_SPL_CPU=y
 CONFIG_SPL_FS_EXT4=y
-CONFIG_SPL_RTC_SUPPORT=y
+CONFIG_SPL_RTC=y
 CONFIG_SYS_PROMPT="openpiton$ "
 # CONFIG_CMD_CPU is not set
 CONFIG_CMD_BOOTZ=y