Migrate CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC

This converts CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC to Kconfig

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
diff --git a/configs/cm_t335_defconfig b/configs/cm_t335_defconfig
index 46979b3..45eace2 100644
--- a/configs/cm_t335_defconfig
+++ b/configs/cm_t335_defconfig
@@ -19,6 +19,7 @@
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_MTD_SUPPORT=y
 CONFIG_SPL_POWER_SUPPORT=y
+# CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC is not set
 CONFIG_SYS_PROMPT="CM-T335 # "
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_EEPROM=y