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_crane_defconfig b/configs/am3517_crane_defconfig
index 42260b1..516ac2d 100644
--- a/configs/am3517_crane_defconfig
+++ b/configs/am3517_crane_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SYS_TEXT_BASE=0x80100000
 # CONFIG_SPL_GPIO_SUPPORT is not set
 CONFIG_TARGET_AM3517_CRANE=y
+CONFIG_EMIF4=y
 CONFIG_BOOTDELAY=10
 CONFIG_SPL=y
 # CONFIG_SPL_EXT_SUPPORT is not set