Convert CONFIG_EMIF4 et al to Kconfig

This converts the following to Kconfig:
   CONFIG_EMIF4
   CONFIG_SDRC

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefano Babic <sbabic@denx.de>
diff --git a/configs/am3517_evm_defconfig b/configs/am3517_evm_defconfig
index b3e89eb..920c61c 100644
--- a/configs/am3517_evm_defconfig
+++ b/configs/am3517_evm_defconfig
@@ -5,6 +5,7 @@
 CONFIG_TI_COMMON_CMD_OPTIONS=y
 # CONFIG_SPL_GPIO_SUPPORT is not set
 CONFIG_TARGET_AM3517_EVM=y
+CONFIG_EMIF4=y
 CONFIG_BOOTDELAY=10
 CONFIG_VERSION_VARIABLE=y
 CONFIG_SPL=y