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/arch/arm/mach-omap2/omap3/Kconfig b/arch/arm/mach-omap2/omap3/Kconfig
index cc2c4cd..11f5f05 100644
--- a/arch/arm/mach-omap2/omap3/Kconfig
+++ b/arch/arm/mach-omap2/omap3/Kconfig
@@ -150,6 +150,21 @@
 
 endchoice
 
+choice
+	prompt "Memory Controller"
+	default SDRC
+
+config SDRC
+	bool "SDRC controller"
+	help
+	  The default memory controller on most OMAP3 boards is SDRC.
+
+config EMIF4
+	bool "EMIF4 controller"
+	help
+	  Enable this on boards like AM3517 which use EMIF4 controller
+endchoice
+
 config SPL_OMAP3_ID_NAND
 	bool "Support OMAP3-specific ID and MFR function"
 	help