Convert CONFIG_SYS_FSL_ESDHC_HAS_DDR_MODE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FSL_ESDHC_HAS_DDR_MODE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/pico-imx6_defconfig b/configs/pico-imx6_defconfig
index 086b3ee..45f72d7 100644
--- a/configs/pico-imx6_defconfig
+++ b/configs/pico-imx6_defconfig
@@ -72,6 +72,7 @@
 CONFIG_FASTBOOT_FLASH=y
 CONFIG_FASTBOOT_FLASH_MMC_DEV=0
 CONFIG_SUPPORT_EMMC_BOOT=y
+CONFIG_SYS_FSL_ESDHC_HAS_DDR_MODE=y
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_ATHEROS=y