Convert CONFIG_RTC_DS1337 et al to Kconfig

This converts the following to Kconfig:
   CONFIG_RTC_DS1337
   CONFIG_RTC_DS1337_NOOSC
   CONFIG_RTC_DS1338
   CONFIG_RTC_DS1374
   CONFIG_RTC_DS3231
   CONFIG_RTC_MC13XXX
   CONFIG_RTC_MXS
   CONFIG_RTC_PT7C4338

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_NAND_defconfig b/configs/P2020RDB-PC_NAND_defconfig
index 9b4ca39..4f22e24 100644
--- a/configs/P2020RDB-PC_NAND_defconfig
+++ b/configs/P2020RDB-PC_NAND_defconfig
@@ -146,6 +146,7 @@
 CONFIG_TSEC_ENET=y
 CONFIG_PCIE_FSL=y
 CONFIG_DM_RTC=y
+CONFIG_RTC_PT7C4338=y
 CONFIG_SYS_NS16550_SERIAL=y
 CONFIG_SPL_NS16550_MIN_FUNCTIONS=y
 CONFIG_SPI=y