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/twister_defconfig b/configs/twister_defconfig
index 7bbf781..53edadb 100644
--- a/configs/twister_defconfig
+++ b/configs/twister_defconfig
@@ -3,6 +3,7 @@
 CONFIG_ARCH_OMAP2PLUS=y
 CONFIG_SYS_TEXT_BASE=0x80008000
 CONFIG_TARGET_TWISTER=y
+CONFIG_EMIF4=y
 CONFIG_BOOTDELAY=10
 CONFIG_SPL=y
 # CONFIG_SPL_EXT_SUPPORT is not set