armv8/ls2085a_emu: Drop DDR3 emulation target

The emulator with DDR3 model was used during model bringup. DDR4
controllers are used with ls2085a. Drop the DDR4 target defconfig
and enable DDR4 in ls2085a_emu_defconfig.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/configs/ls2085a_emu_defconfig b/configs/ls2085a_emu_defconfig
index fa4a44e..9c82e17 100644
--- a/configs/ls2085a_emu_defconfig
+++ b/configs/ls2085a_emu_defconfig
@@ -1,6 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_LS2085A_EMU=y
-CONFIG_SYS_EXTRA_OPTIONS="EMU"
+CONFIG_SYS_EXTRA_OPTIONS="EMU,SYS_FSL_DDR4"
 # CONFIG_CMD_CONSOLE is not set
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_XIMG is not set